* winsup.h: Define MAX_SID_LEN and new MAX_HOST_NAME.

    * winsup.h: Define MAX_SID_LEN and new MAX_HOST_NAME.
        * fork.cc (fork): Use above defines instead of numerical constants.
        * shared.cc (sec_user): Ditto.
        * shared.h (class pinfo): Ditto.
        * syscall.cc (seteuid): Ditto.
        * spawn.cc (_spawnve): Ditto. Eliminate conditional.
        (spawn_guts): Set child->uid = USHRT_MAX when user context will be
        changed in child process.
        * uinfo.cc (uinfo_init): Check for myself->uid instead of myself->psid
        to avoid reloading of /etc/passwd on process startup if ntsec is off.
        Use above defines instead of numerical constants.
        * security.cc: Move define for MAX_SID_LEN to winsup.h.