(lwpInitSelect): The code to query the system's limit on file

(lwpInitSelect): The code to query the system's limit on file
descriptors was not portable.  Simply use FD_SETSIZE instead.  The
lower of the two applies, so this wastes storage if the system's limit
is significantly below FD_SETSIZE.  Not an issue, as FD_SETSIZE is
fairly small.
(lwpSleepFd): Return if fd is too large.  Returning isn't nice,
but better than the buffer overruns in the old code.
(lwpSelect): Member nfile unused, remove.