libtextstyle: Don't use an external libcroco.
* gnulib-local/m4/libcroco.m4 (gl_LIBCROCO): Accept an optional FORCE-INCLUDED
argument.
* libtextstyle/gnulib-local/modules/libcroco.diff: New file.
* libtextstyle/autogen.sh: Pass another --local-dir option to gnulib-tool.
