Add Haskell types for C types useconds_t and suseconds_t, which are respectively CUSeconds and CSUSeconds.

The tv_usec field of struct timeval was incorrectly used as C type time_t; the actual C type is suseconds_t. On OS X, time_t is longer than suseconds_t, which caused garbage bits to be copied as reported in trac #4247 and #4970. This patch is part 1 of 4 to fix those tickets.