Patches for GTK 2. Puzzles already _built_ under GTK 2, but now it

Patches for GTK 2. Puzzles already _built_ under GTK 2, but now it
builds better:
 - the GTK makefile now defines $(GTK_CONFIG) which you can
   override, so you can build for GTK 2 with no makefile-editing
   simply by running `make GTK_CONFIG="pkg_config gtk+-2.0"'
 - we use Pango to find appropriate fonts, which means the text in
   the puzzles actually (gasp!) adapts its size to the
   circumstances. Unfortunately, I've been unable to do this
   portably without depending on _either_ a Pango function that
   isn't present in older versions _or_ the underlying window system
   being X11; I'd appreciate someone doing better.

[originally from svn r5693]