README.Git: Update to newest Gnulib.

This should fix build failures on OpenSUSE, OpenBSD, and possibly on other
platforms that have libintl but on which libintl does not contain a
definition of __printf__, by integrating the following commit:

    commit a43e24168368619e2d51fe7a37abc4969d7a87fe
    Author: Bruno Haible <bruno@clisp.org>
    Date:   Sun May 16 14:16:03 2010 +0200

        Fix collision between gnulib's and libintl's printf replacements.