update disulphide test to work with ensemble branch
add in template instantiations that work for gcc x86_64 

contribution from Hoi Tik Alvin Leung this ensures compilation includes
all the templates used in each shared object. It is most probably over
eager in what it compiles and could cause shared library bloat. However,
the overhead should be relatively small as shown by the shared library
sizes:

572K	_PyEnsemblePotProxy.so
364K	pyEnsemblePot.so
620K	_xPyPot.so

this closes the ticket #43 'undefined variables in _xPyPot.so'