manual: Replace summary.awk with summary.pl.

manual: Replace summary.awk with summary.pl.

The Summary is now generated from @standards, and syntax-checking is
performed.  If invalid @standards syntax is detected, summary.pl will
fail, reporting all errors.  Failure and error reporting is disabled
for now, however, since much of the manual is still incomplete
wrt. header and standards annotations.

Note that the sorting order of the Summary has changed; summary.pl
respects the locale, like summary.awk did, but the use of LC_ALL=C is
introduced in the Makefile.  Other notable deviations are improved
detection of the annotated elements' names, which are used for
sorting, and improved detection of the @node used to reference into
the manual.  The most noticeable difference in the rendered Summary is
that entries may now contain multiple lines, one for each header and
standard combination.

summary.pl accepts a `--help' option, which details the expected
syntax of @standards.  If errors are reported, the user is directed to
this feature for further information.

	* manual/Makefile: Generate summary.texi with summary.pl.
	Force use of the C locale.  Update Perl dependency comment.
	* manual/header.texi: Update reference to summary.awk.
	* manual/macros.texi: Refer authors to `summary.pl --help'.
	* manual/summary.awk: Remove file.
	* manual/summary.pl: New file.  Generate summary.texi, and
	check for @standards-related syntax errors.
	* manual/argp.texi: Convert header and standards @comments to
	@standards.
	* manual/arith.texi: Likewise.
	* manual/charset.texi: Likewise.
	* manual/conf.texi: Likewise.
	* manual/creature.texi: Likewise.
	* manual/crypt.texi: Likewise.
	* manual/ctype.texi: Likewise.
	* manual/debug.texi: Likewise.
	* manual/errno.texi: Likewise.
	* manual/filesys.texi: Likewise.
	* manual/getopt.texi: Likewise.
	* manual/job.texi: Likewise.
	* manual/lang.texi: Likewise.
	* manual/llio.texi: Likewise.
	* manual/locale.texi: Likewise.
	* manual/math.texi: Likewise.
	* manual/memory.texi: Likewise.
	* manual/message.texi: Likewise.
	* manual/pattern.texi: Likewise.
	* manual/pipe.texi: Likewise.
	* manual/process.texi: Likewise.
	* manual/resource.texi: Likewise.
	* manual/search.texi: Likewise.
	* manual/setjmp.texi: Likewise.
	* manual/signal.texi: Likewise.
	* manual/socket.texi: Likewise.
	* manual/startup.texi: Likewise.
	* manual/stdio.texi: Likewise.
	* manual/string.texi: Likewise.
	* manual/sysinfo.texi: Likewise.
	* manual/syslog.texi: Likewise.
	* manual/terminal.texi: Likewise.
	* manual/threads.texi: Likewise.
	* manual/time.texi: Likewise.
	* manual/users.texi: Likewise.