Log Message:
Updated flex to 2.6.3.

* version 2.6.3 released 2016-12-30

** scanner

*** several bug fixes resolved problems introduced in recent flex
    versions regarding processing of comments, literals and various
    quoting scenarios.

*** If the path to m4 was sufficiently long, a buffer overflow could
    occur. This has been resolved. The fix also removes dependence on
    the constant PATH_MAX.

** build

*** A new configure option --disable-bootstrap changes the behavior of
    the build system when building flex. The default
    "--enable-bootstrap" behavior is to build flex, then to use that
    flex to build flex again. With --disable-bootstrap, the scanner is
    simply built by sedding the scanner source. This is friendlier to
    cross compilation.

*** The compatibility functions in lib/ are no longer built as a
    library. Instead, they are built as $(LIBOBJ) objects. This is
    simpler and friendlier to cross compilation.

*** It is now possible to build flex without building the accompanying
    libfl. This is friendlier to cross compilation. See the
    --disable-libfl option to configure. Resolves #99.

*** the PIC version of libfl was not correctly built. It is no longer
    included in the build/installation targets of flex since it was
    unused.

*** the distributed man page is only rebuilt when the relevant source
    files change or when the binary doesn't exist. In particular, this
    is friendlier to cross compilation. Resolves #108

** test

*** the shell scripts in the test suite are more portable across different shell \ 
implementations.