* Makefile.am: install gimp.m4 too

* libgimp/gimpprotocol.[ch]
* libgimp/gimp.c
* app/plug_in.[ch]
* app/procedural_db.c: exported the gdisplay ID to the plugins, so they can
be smart about hooking on to status bars in the appropriate display shell

* libgimp/Makefile.am
* libgimp/gimp.c: make the plugins aware of $gimpdir for gtkrc parsing

-Yosh