Xpra: Ticket #974: xpra clients 16.0 r10472 and r10504 do not launch

The xpra clients 0.16.0-r10472 and 0.16.0-r10504 downloaded from http://xpra.org/beta/osx/ could not be launched.

This is the error I'm getting when I try to launch them from MAC OSX 10.10.3:

Kenneth-Baker:Desktop maint$ cd xpra-16.0-r10472/Xpra.app/Contents/MacOS/
Kenneth-Baker:MacOS maint$ ./xpra attach tcp:10.0.32.147:2200
ImportError: could not import gtk
Fatal Python error: can't initialize module gtkosx_application:
Abort trap: 6
Kenneth-Baker:MacOS maint$

Kenneth-Baker:Desktop maint$ cd xpra-16.0-r10504/Xpra.app/Contents/MacOS/
Kenneth-Baker:MacOS maint$ ./xpra attach tcp:10.0.32.147:2200
ImportError: could not import gtk
Fatal Python error: can't initialize module gtkosx_application:
Abort trap: 6
Kenneth-Baker:MacOS maint$