Relax AC_INIT requirements for PACKAGE and VERSION strings again.
* lib/m4sugar/m4sh.m4 (AS_LITERAL_HEREDOC_IF): New macro.
(_AS_LITERAL_HEREDOC_IF, _AS_LITERAL_HEREDOC_IF_YES)
(_AS_LITERAL_HEREDOC_IF_NO): New helper macros.
* lib/autoconf/general.m4 (_AC_INIT_PACKAGE): Use
AS_LITERAL_HEREDOC_IF for PACKAGE and VERSION strings.
* tests/base.at (AC_INIT with unusual version strings): New test.
* tests/m4sh.at (AS@&t@_LITERAL_IF): Extend test.
* NEWS: Update.
Signed-off-by: Eric Blake <eblake@redhat.com>