Fix python wrapping bug.
Fix python wrapping bug.

The _opensim target needs the source output of the PyWrap target. There was a bug in the CMakeLists that caused the _opensim target not to depend on this source output unless CMake was re-run after PyWrap was build.

Also added a fix to get python wrapping working on APPLE Mac OS X, and improved error handling.
opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core