> *** The test program failed to compile or link. See the file config.log
> for the

See the file config.log

> *** exact error that occured. This usually means GTK+ is incorrectly
> installed.
> configure: error: Test for GTK+ failed. See the file 'INSTALL' for help.

The config.log is usually under your WRKSRC directory, like work*/gimp*. 
Look for the related lines -- I normally start from the bottom of the file 
and work my way up (as the top of the file has unrelated and non-important 
errors).

Jeremy C. Reed