Log Message:
Update to 2.64.

XXX: Needs m4>=1.4.6, but we use USE_TOOLS+=gm4:run, and I don't see
a way to specify a version there. Please someone fix that :)
On the other hand, 1.4.6 was added to pkgsrc in 09/2006, so I hope
everyone has it by now.

* Major changes in Autoconf 2.64 (2009-07-26) [stable]
  Released by Eric Blake, based on git versions 2.63b.*.

** Autoconf now requires GNU M4 1.4.6 or later.  Earlier versions of M4
   have a bug in regular expression handling that interferes with some
   of the speedups provided since Autoconf 2.63.  GNU M4 1.4.13 or
   later is recommended.

** AS_IF and AS_CASE have been taught to avoid syntax errors even when
   given arguments that expand to just whitespace.

** The following documented autoconf macros are new:
   AC_ERLANG_SUBST_ERTS_VER

** The autoheader tool now understands m4 macro arguments passed to
   AC_DEFINE and AC_DEFINE_UNQUOTED.

** Ensure AT_CHECK can support commands that include a # given with
   proper m4 quoting.  For shell comments, this is a new feature; for
   non-shell comments, this fixes a regression introduced in 2.63b.
   Additionally, AT_CHECK correctly supplies shell escapes for
   metacharacters occurring in m4 macro expansions within the expected
   stdout and stderr parameters.

** The macro AT_CHECK now understands the concept of hard failure.  If
   a test exits with an unexpected status 99, cleanup actions for the
   test are inhibited and the test is treated as a failure regardless
   of AT_XFAIL_IF.  It also understands the new directives
   ignore-nolog, stdout-nolog, and stderr-nolog.

** The following documented autotest macros are new:
   AT_CHECK_UNQUOTED  AT_FAIL_IF  AT_SKIP_IF

** The following documented m4sugar macros are new:
   m4_argn  m4_copy_force  m4_default_nblank  m4_default_nblank_quoted
   m4_ifblank  m4_ifnblank  m4_rename_force

** The autoconf testsuite now exercises all Erlang macros.

* Major changes in Autoconf 2.63b (2009-03-31) [beta]
  Released by Eric Blake, based on git versions 2.63.*.

** The manual is now shipped under the terms of the GNU FDL 1.3.

** AC_REQUIRE now detects the case of an outer macro which first expands
   then later indirectly requires the same inner macro.  Previously,
   this case led to silent out-of-order expansion (bug present since
   2.50); it now issues a syntax warning, and duplicates the expansion
   of the inner macro to guarantee dependencies have been met.  See
   the manual for advice on how to refactor macros in order to avoid
   the bug in earlier autoconf versions and avoid increased script
   size in the current version.

** AC_DEFUN_ONCE has improved semantics.  Previously, a macro declared
   with AC_DEFUN_ONCE warned on a second invocation; and out-of-order
   expansion was still possible.  Now, dependencies are guaranteed,
   and subsequent invocations are a silent no-op.  This makes
   AC_DEFUN_ONCE an ideal macro for silencing AC_REQUIRE warnings.

** The following macros are now defined with AC_DEFUN_ONCE.  This means
   a subtle change in semantics; previously, an AC_DEFUN macro could
   expand one of these macros multiple times or surround the macro
   inside shell conditional text to bypass the effects of these
   macros, but now the macro will expand exactly once, and prior to
   the start of any enclosing AC_DEFUN macro:
   AC_CANONICAL_BUILD  AC_CANONICAL_HOST  AC_CANONICAL_TARGET
   AC_HEADER_ASSERT  AC_PROG_INSTALL  AC_PROG_MKDIR_P
   AC_USE_SYSTEM_EXTENSIONS

** AC_LANG_ERLANG works once again (regression introduced in 2.61a).

** AC_HEADER_ASSERT is fixed so that './configure --enable-assert' no
   longer mistakenly disables assertions.

** AC_INIT now takes an optional fifth parameter that can be used to
   set AC_PACKAGE_URL, a URL for the package's home page; the URL is
   used in `configure --help' and is also available via AC_DEFINE.

** Autotest testsuites accept an option --jobs[=N] for parallel testing.
   This feature is still in testing, and may not work on every
   platform, help in improving it would be appreciated.

** Autotest testsuites do not attempt to write startup error messages
   to the log file before that is opened (regression introduced in 2.63).

** Configure scripts now use shell functions.  This feature leads to
   smaller configure files and faster execution.

** Present But Cannot Be Compiled: Autoconf will now proceed with
   the compiler's result if a header is present but cannot be compiled.
   The warning is still printed, and you should really fix it by
   providing a fourth parameter to AC_CHECK_HEADER/AC_CHECK_HEADERS.

** Autoreconf added aclocal to the set of programs affected by the
   `autoreconf -I dir' option.

** The following documented m4sugar macros are new:
   m4_chomp  m4_chomp_all  m4_cleardivert  m4_curry  m4_default_quoted
   m4_esyscmd_s  m4_map_args  m4_map_args_pair  m4_map_args_sep
   m4_map_args_w  m4_set_map  m4_set_map_sep  m4_stack_foreach
   m4_stack_foreach_lifo  m4_stack_foreach_sep
   m4_stack_foreach_sep_lifo

** The following m4sugar macros are documented now, but in some cases
   with slightly different semantics than what the previous
   undocumented version had:
   m4_copy  m4_dumpdefs  m4_rename  m4_version_prereq

** The m4sugar macro m4_expand has been taught to handle unterminated
   comments and shell case statements.  As a result, it is used
   internally in more places, such as AC_DEFINE and AT_CHECK.  Most
   uses of AC_DEFINE and AT_CHECK should not behave any differently;
   however, it may be necessary to add double-quoting around
   unbalanced `(' where single-quoting used to be sufficient.

** The following documented m4sh macros are new:
   AS_INIT_GENERATED  AS_LINENO_PREPARE  AS_ME_PREPARE  AS_SET_STATUS
   AS_VAR_APPEND  AS_VAR_ARITH  AS_VAR_COPY

** The following m4sh macros are documented now, but in some cases
   with slightly different semantics than what the previous
   undocumented version had:
   AS_ECHO  AS_ECHO_N  AS_ESCAPE  AS_EXIT  AS_LITERAL_IF  AS_UNSET
   AS_VAR_IF  AS_VAR_POPDEF  AS_VAR_PUSHDEF  AS_VAR_SET  AS_VAR_SET_IF
   AS_VAR_TEST_SET  AS_VERSION_COMPARE

** The m4sh macros AS_IF and AS_CASE can now be used in shell lists.
   The responsibility for supplying a trailing newline now belongs to
   the call site, but since most users did not add dnl, this generally
   results in fewer empty lines in configure.