We can now build and run pidgin on OSX.
Pidgin requires an X11 server to run.
* Build: Differences Linux and OSX now parameterized
* Darwin: build against gtk2-x11 instead of gtk
* Darwin: disable gtkspell2 (spellcheck)
* Darwin: disable farstream (voice and video)
Signed-off-by: Frederick F. Kautz IV <fkautz@alumni.cmu.edu>