Update Xcode Project ([3520119] by Andy Maloney)

This patch updates the Xcode project from git 93c3723da5b43403422bf2ea0d709d6ebb06f143.

It does the following:

- add/remove include files to the project since they moved
- add/remove the OGRE files to the project since they changed
- removes the _GLIBCXX defines since they are no longer used
- sets the compiler to LLVM GCC 4.2
- sets the SDK to Mac OS X 10.5 so it will build on 10.5 and 10.6
- removes the PPC-related VALID_ARCHS

This means it's set up for Mac OS X 10.5 and higher and will build a 32/64-bit universal lib by default.

I didn't touch any Boost-related stuff since I'm not using it, but it should be just a matter of updating the included libs with whatever version you have installed.

git-svn-id: https://assimp.svn.sourceforge.net/svnroot/assimp/trunk@1242 67173fc5-114c-0410-ac8e-9d2fd5bffc1f