Ghost Context Refactor

https://developer.blender.org/D643
Separates graphics context creation from window code in Ghost so that they can vary separately.

source/gameengine/VideoTexture/SConscript

@@ -37,7 +37,8 @@ incs = [
     '#intern/ffmpeg',
     '#intern/guardedalloc',
     '#intern/string',
-    '#extern/glew/include',
+    env['BF_GLEW_INC'],
+    '#/intern/glew-mx',
     '#intern/moto/include',
     '#source/blender/blenkernel',
     '#source/blender/blenlib',
@@ -57,7 +58,8 @@ incs = [
     ]
 incs = ' '.join(incs)
 
-defs = ['GLEW_STATIC'] 
+defs = env['BF_GL_DEFINITIONS']
+
 if env['OURPLATFORM'] in ('win32-vc', 'win64-vc','win32-mingw', 'win64-mingw'):
     if env['BF_DEBUG']:
         defs.append('_DEBUG')