Fallback for manual setup of GTK 1, if autoconf is run on a system
where the GTK1 detection function AM_PATH_GTK hasn't been provided by
/usr/share/aclocal/gtk.m4 or equivalent.

(Systems without gtk.m4 are becoming more common, but on the other
hand I know at least one person is still using GTK 1 PuTTY since the
0.62 release.)


git-svn-id: svn://svn.tartarus.org/sgt/putty@9868 cda61777-01e9-0310-a592-d414129be87e