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

po/.gitignore

@@ -1,22 +1,22 @@
-*.gmo
-*.po
-*.po~
-.reference
-LINGUAS
-Makefile
-Makefile.in
-Makefile.in.in
-Makevars
-Makevars.template
-POTFILES
-Rules-quot
-bison.pot
-boldquot.sed
-en@boldquot.header
-en@quot.header
-insert-header.sed
-insert-header.sin
-quot.sed
-remove-potcdate.sed
-remove-potcdate.sin
-stamp-po
+/*.gmo
+/*.po
+/*.po~
+/.reference
+/LINGUAS
+/Makefile
+/Makefile.in
+/Makefile.in.in
+/Makevars
+/Makevars.template
+/POTFILES
+/Rules-quot
+/bison.pot
+/boldquot.sed
+/en@boldquot.header
+/en@quot.header
+/insert-header.sed
+/insert-header.sin
+/quot.sed
+/remove-potcdate.sed
+/remove-potcdate.sin
+/stamp-po