[OGRE-355] Fix OS X build with PCH on Xcode 4.
[OGRE-355] Fix OS X build with PCH on Xcode 4.

--HG--
branch : v1-9

jhu-lcsr-forks/ogre,jhu-lcsr-forks/ogre,jhu-lcsr-forks/ogre,jhu-lcsr-forks/ogre,jhu-lcsr-forks/ogre