FreeBSD-SA00:42.
Change stackgap_alloc to bounds-check the allocation vs. the stack
gap, returning NULL if there isn't room for the allocation.
Change emul_find() to check for a NULL return from stackgap_alloc()
and convert that into ENAMETOOLONG.
Reorder various emulation syscalls so that all *_CHECK_ALT_{EXIST,CREAT}
calls (which turn into emul_find() under the covers come *after* small,
fixed-size stackgap_alloc() calls.
Clean up ibcs2 {get,set}groups.
6b88a0fc51