* DEPENDENCIES: Mention the requirement.

* gnulib-tool (DEFAULT_AUTOCONF_MINVERSION): Bump to 2.63.
(func_get_filelist): Don't list m4/onceonly.m4 any more.
* pygnulib/GLModuleSystem.py (getFiles): Likewise.
* m4/onceonly.m4: Remove file.

* m4/openmp.m4: Remove file.
* modules/openmp (Files): Remove m4/openmp.m4.

* m4/configmake.m4 (gl_CONFIGMAKE_PREP): Don't set datarootdir, docdir,
htmldir, dvidir, pdfdir, psdir, localedir.
* m4/po.m4 (AM_PO_SUBDIRS): Don't set localedir.

* m4/gnulib-common.m4 (m4_foreach_w): Remove fallback for
Autoconf < 2.60.
(AC_PROG_MKDIR_P): Remove definition for Autoconf < 2.62.
(AC_PROG_SED): Remove fallback for Autoconf < 2.60.

* m4/errno_h.m4 (AC_COMPUTE_INT): Remove fallback for Autoconf < 2.61.
* m4/size_max.m4 (AC_COMPUTE_INT): Likewise.
* m4/stdint.m4 (AC_COMPUTE_INT): Likewise.

* m4/fcntl-o.m4 (gl_FCNTL_O_FLAGS): Assume AC_USE_SYSTEM_EXTENSIONS
exists.
* m4/threadlib.m4 (gl_THREADLIB_EARLY_BODY): Likewise,

* m4/lib-link.m4 (AC_LIB_LINKFLAGS_BODY): Remove workaround for
Autoconf < 2.61.

* m4/lib-prefix.m4 (AC_LIB_ARG_WITH): Remove macro.
(AC_LIB_PREFIX): Use AC_ARG_WITH, assuming semantics of
Autoconf >= 2.52.

* m4/longlong.m4: Require Autoconf >= 2.62. Update comments.
* m4/ls-mntd-fs.m4: Require Autoconf >= 2.60. Update comments.
* m4/gettext.m4 (AM_GNU_GETTEXT): Update comment.