Call MPI_Abort() from the terminate_handler() to take care of
implementations which do not unwind the stack (and therefore
never make it to the LibMeshInit destructor).

Write tracefiles from libmesh_error() when running in parallel,
but only if --enable-tracefiles is set during configure.
Merge pull request #131 from libMesh/terminate_handler

Call MPI_Abort() from the terminate_handler() to take care of