This solves issue #66

Return error value of pytest and fix location of wrapper.so to make the
relative imports in python work.

This ensures that the extension that is locally built is always found
first instead of potentially loading already existing modules in the
path.

cython command now works for VPATH builds, test script fixed

precision_typedefs.h is needed by the generalized methods, but only
included when built with MPI. Thus the normal distcheck does not catch
this.

For this, dlopen needs to share symbols globally because MKL internally
uses dynamic loading that doesn't work otherwise.

Add parts to configure.ac and Makefile.am. There is now an additional
flag --enable-python-tests. The tests require the pytest package.

The implementation of the test is a bit hacky because it takes
wrapper.so from .libs. This should probably improbed for better
portability.