New module 'time', so that apps can include <time.h> as per

New module 'time', so that apps can include <time.h> as per
POSIX and GNU instead of separate include files like time_r.h
and timegm.h.  This implementation tries out a simpler approach
for replacing decls in standard include files (as compared to
the string module), somewhat as an experiment.

* config/srclist.txt: Comment out mktime.c for now.
* doc/gnulib-tool.texi (Initial import): Don't use time_r as an example
since it doesn't apply any more.  Use generic wording instead.
* MODULES.html.sh (Support for systems lacking POSIX:2001): New module
'time'.
* lib/time_.h, m4/time_h.m4, modules/time: New files.
* lib/strptime.h, lib/time_r.h, lib/timegm.h: Remove.
* lib/mktime.c: Include config.h depending on _LIBC, not HAVE_CONFIG_H.
Don't include <sys/types.h>; no longer needed since we assume C89.
* lib/mktime.c: Don't include "time_r.h"; no longer needed.
* lib/strftime.c: Likewise.
* lib/time_r.c: Likewise.
* lib/nanosleep.c (nanosleep): #undef after include files, not before.
* lib/nanosleep.c: Include <time.h> first, to check interface.
* lib/strptime.c: Likewise.
* lib/time_r.c: Likewise.
* lib/timegm.c: Likewise.
* lib/strptime.c: Don't include strptime.h or time_r.h; no longer
needed.
* lib/timegm.c: Don't include timegm.h; no longer needed.
* lib/timespec.h: Don't include <sys/time.h> before <time.h>;
time.h now handles any problems in that area.
(struct timespec, nanosleep): Remove; time.h now arranges for these.
* lib/xnanosleep.c: Don't include timespec.h; no longer needed now
that time.h defines struct timespec.
* m4/nanosleep.m4 (gl_FUNC_NANOSLEEP): Check that nanosleep is declared.
Set REPLACE_NANOSLEEP.  Don't AC_DEFINE nanosleep; the time module now
handles that.
* m4/strptime.m4 (gl_FUNC_STPRTIME): Set REPLACE_STRPTIME.
* m4/time_r.m4 (gl_TIME_R): Don't define HAVE_TIME_R_POSIX; no longer
needed.  Set REPLACE_LOCALTIME.
* m4/timegm.m4 (gl_FUNC_TIMEGM): Set REPLACE_TIMEGM.
* m4/timespec.m4 (gl_CHECK_TYPE_STRUCT_TIMESPEC): Move to time_h.m4.
(gl_TIMESPEC): Don't check for sys/time.h or struct timespec or
nanosleep; time_h.m4 now does that.  Don't require
gl_USE_SYSTEM_EXTENSIONS; no longer needed directly, and the time
module handles this now.
* modules/getdate (Depends-on): Remove timespec.  Add time.
* modules/nanosleep (Depends-on): Likewise.
* modules/stat-time (Depends-on): Likewise.
* modules/nanosleep (Include): Include time.h, not timespec.h.
* modules/strptime (Files): Remove lib/strptime.h.
(Depends-on): Add extensions, time.
(Include): Include time.h, not strptime.h.
* modules/time_r (Files): Remove lib/time_r.h.
(Depends-on): Add time.
(Include): Include time.h, not time_r.h.
* modules/timegm: Likewise.
* modules/timespec (Description): Now does timespec-related decls
of our own, instead of struct timespec itself.
(Depends-on): Add time; remove extensions.
(Maintainer): Add self.
* modules/utimecmp (Depends-on): Add time; remove timespec.
* modules/utimens (Depends-on): Likewise.
* modules/xnanosleep (Depends-on): Likewise.