OSX 10.8 - fix building java bindings 

Building java bindings fails on OSX 10.8 because it can
not locate system headers. This is caused by the ant task
looking for OSX SDKs in their old location.

This fixes it by first looking for the SDKs in their new location
inside XCode's app bundle.  On older systems that will fail and the code
will revert back to looking inside the old SDK location.