Fixed: Changing previous update to libmei Xcode project

It seems building the library with the target at 10.8 creates problems with building the Python module, since there would be a library mismatch between a 10.9-built Python and a version of the MEI framework built for 10.8.

So, in the interim: If you want to run the C++ tests, switch your Xcode target to 10.8; otherwise, you can leave it at 10.9