remove pyopencl.np. pypy have already switched to numpy and most of the part cannot run on numpypy anyway....

Fix some problem when installing under pypy.

Make get_devices() return an empty list instead of erroring out (reported by Tomasz Rybak on the master branch)

Conflicts:
	.gitignore
	src/wrapper/wrap_cl.hpp

Use the documented struct.calcsize to determine machine word size for better pypy support.