The same case is already covered by test_array.py and doesn't have to be covered here again.

fix test_wrapper.test_get_info for old opencl version, adapted from the cffi branch ac7ed3c9

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

FIX: no more explicit padding required for vectors

Additionally, relying on default values for initialization triggers a
deprecation warning. Added three more vector constructors: filled_ which fills
the entire vector with a given value, zeros_ and ones_.

Closes #28

Typo fix.