Log Message:
Update to 4.2:

* now released under GPLv3

* added a new extension `z` to clear pattern space even in the presence
of invalid multibyte sequences

* a preexisting GNU gettext installation is needed in order to compile
GNU sed with NLS support

* new option --follow-symlinks, available when editing a file in-place.
This option may not be available on some systems (in this case, the
option will *not* be a no-op; it will be completely unavailable).
In the future, the option may be added as a no-op on systems without
symbolic links at all, since in this case a no-op is effectively
indistinguishable from a correct implementation.

* hold-space is reset between different files in -i and -s modes.

* multibyte processing fixed

* the following GNU extensions are turned off by --posix: options [iImMsSxX]
in the `s' command, address kinds `FIRST~STEP' and `ADDR1,+N' and `ADDR1,~N',
line address 0, `e' or `z' commands, text between an `a' or `c' or `i'
command and the following backslash, arguments to the `l' command.
--posix disables all extensions to regular expressions.

* fixed bug in 'i\' giving a segmentation violation if given alone.

* much improved portability

* much faster in UTF-8 locales

* will correctly replace ACLs when using -i

* will now accept NUL bytes for `.'