Deactivate GL_FRAGMENT_SHADER_ATI before deactivating a context

[Milan Kostić]

I'm use Mesa 7.01 because that version not have this problem (I try
fragshader.c test from bug #15269). Bug is introduced earler with this
commit, i'm warn about it but nobody listen because i'm not offering
good solution:
 http://gitweb.freedesktop.org/?p=mesa/mesa.git;a=commit;h=e279a0a076b7a3c8d6...

 Also with that commit several other regressions was introduced with
r200 DRI driver. Maybe they will listen someone (Stefan:)) from here.