Fix test srcdir

Fixes #68.

Note I had to reorder `MPI_Abort()` and `queso_error()` in `Defines.h`.  Calling `queso_error()` after `MPI_Abort` is a no-op.  This may lead to uncaught exceptions which in turn means that `MPI_Abort` is not called and processes still go about their business when they shouldn't.  We'll need to check for uncaught exceptions and call `MPI_Abort` if this is the case.