smaller (level_num) needed to be cast to the larger (flags{..]) since
the flag really held a number greater than 32 bits.)
Added CYGWIN test to allow definition of PTHREAD_MUTEX_ERRORCHECK_NP
and friends so cygwin compilation could get further. Teri has a
comment just before this change (line 217 in thread_xsb.h) which
sounds relevant, but I don't understand it. Is this what was meant?
Or was it to say that this change of mine is probably wrong?
