BSDI specific patches, inspired by Nigel Head and otto@mail.olympus.net.

Also (non-BSDI specific):

- Change the CHECK_STATUS() macro so it tests for nonzero error codes
instead of negative error codes only (this was needed for BSDI, but
appears to be correct according to the PTHREADS spec).

- use memset() to zero out the allocated lock structure.  Again, this
was needed for BSDI, but can't hurt elsewhere either.