maint: re-anchor all .gitignore entries.

* bootstrap: Copy from gnulib's latest for the fix to
automatically anchor entries it constructs.
* gnulib: Update to latest just so it has the same bootstrap.
* .gitignore, build-aux/.gitignore, doc/.gitignore:
* lib/.gitignore, m4/.gitignore, po/.gitignore:
* runtime-po/.gitignore: Re-anchor all entries.
(cherry picked from commit e503b9cbbe)

Conflicts:

    build-aux/.gitignore
    doc/.gitignore
    src/.gitignore

.gitignore

@@ -1,32 +1,32 @@
-.tarball-version
-.version
 /*.cache
 /*.flc
 /*.prj
 /*~
+/.tarball-version
+/.version
+/ABOUT-NLS
+/COPYING
+/GNUmakefile
+/INSTALL
+/Makefile
+/Makefile.in
 /_*
-ABOUT-NLS
-COPYING
-GNUmakefile
-INSTALL
-Makefile
-Makefile.in
-a.exe
-a.out
-aclocal.m4
-b.out
-bison-*
-conf[0-9]*
-confdefs*
-config.log
-config.status
-configure
-configure.lineno
-conftest*
-gnulib
-javacomp.sh
-javaexec.sh
-maint.mk
-patches
-releases
-stamp-h*
+/a.exe
+/a.out
+/aclocal.m4
+/b.out
+/bison-*
+/conf[0-9]*
+/confdefs*
+/config.log
+/config.status
+/configure
+/configure.lineno
+/conftest*
+/gnulib
+/javacomp.sh
+/javaexec.sh
+/maint.mk
+/patches
+/releases
+/stamp-h*