build: drop the 'fixacocal' auxiliary script

The comments in that script state that its use is only required to
work around issues in aclocal from Automake 1.10, while the rest
of the Gettext build infrastructure assumes Automake >= 1.11 anyway.

* autogen.sh: Drop invocations of 'fixaclocal', simply invoke the
'aclocal' program directly.
* build-aux/fixaclocal: Remove.
* Makefile.am (EXTRA_DIST): Stop distributing it.
(ACLOCAL): Drop redefinition in function of 'fixaclocal'.
* gettext-runtime/Makefile.am (ACLOCAL): Likewise.
* gettext-runtime/libasprintf/Makefile.am (ACLOCAL): Likewise.
* gettext-tools/Makefile.am (ACLOCAL): Likewise.
	* gettext-tools/examples/Makefile.am (ACLOCAL): Likewise.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>
Use $(MKDIR_P) instead of obsolete $(mkdir_p).

Suggested by Stefano Lattarini in
<https://lists.gnu.org/archive/html/bug-gettext/2013-04/msg00044.html>.
NEWS: Mention that future 'gettextize' will require Automake 1.10.
Support GtkBuilder file format in the Glade scanner.
Test GtkBuilder UI files extraction support.
NEWS: Document more new features.
Minor clean up for the GtkBuilder support
Fix quoting in gl_LIBXML

* m4/libxml.m4 (gl_LIBXML): Remove extra quotes.
Rename xgettext-gtkbuilder-* tests to xgettext-glade-*.
Make Glade parsing a bit robuster.
Enable python-brace-format detection by default.
NEWS: some wording fixes
Embed gnulib as a git submodule.
Respect only GNULIB_SRCDIR, not GNULIB_TOOL.