[@@inline] is not supported by OCaml 4.01, so remove it.

This caused compilation to fail with a typing error.

I had previously (and incompatibly) changed the overflow behavior
of uint8 and uint16 such that they failed to check for overflow
during arithmatic, and raised Invalid_argument when an overflow
occurred durint their creation (in of_int).  This patch fixes both
of those.

Add tests for coercions of unsigned integers

Deletes commented-out code, fixes naming of ctypes_copy_uint16 and
ctypes_copy_uint8, and adds unit tests.