build: ensure that MKINSTALLDIRS is AC_SUBST-defined

since we're using gettext-0.14.1, which uses that now-obsolete
automake symbol.  Otherwise, make distcheck would fails like this:

    make[2]: Entering directory `/t/libvirt-0.7.6/_build/po'
    /bin/sh @MKINSTALLDIRS@ /t/libvirt-0.7.6/_inst/share
    /bin/sh: @MKINSTALLDIRS@: No such file or directory
    make[2]: *** [install-data-yes] Error 127

* configure.ac (MKINSTALLDIRS): Define.
For reference, we're currently hamstrung by our desire
to support RHEL5, which still uses gettext-0.14:
http://bugzilla.redhat.com/523713

.gnulib @ 11fbc574

-Subproject commit 108cfb803174abf17eb101e9999b9d1a642ce1ba
+Subproject commit 11fbc57405a118e6ec9a3ebc19bbf5ececdae4d6

configure.ac

@@ -1655,6 +1655,11 @@ AM_CONDITIONAL([WITH_LIBVIRTD],[test "x$with_libvirtd" = "xyes"])
 dnl Check for gettext
 AM_GNU_GETTEXT_VERSION([0.14.1])
 AM_GNU_GETTEXT([external])
+dnl Since we're using such an old version of gettext, we must also define
+dnl this symbol, in order to make the autopoint-supplied Makefile.in.in
+dnl work properly.
+AC_SUBST([MKINSTALLDIRS], ["\$(top_builddir)/$ac_aux_dir/mkinstalldirs"])
+
 ALL_LINGUAS=`cd "$srcdir/po" > /dev/null && ls *.po | sed 's+\.po$++'`
 
 dnl Extra link-time flags for Cygwin.