Pull up following revision(s) (requested by mlelstv in ticket #1521):
share/man/man9/kmem.9: revision 1.20 via patch
share/man/man9/vmem.9: revision 1.16
sys/kern/subr_kmem.c: revision 1.62
sys/kern/subr_vmem.c: revision 1.94
fix vmem_alloc() to never return an error for VM_SLEEP requests,
thus fixing kmem_alloc() to never return NULL for KM_SLEEP requests.
instead these operations will retry forever, which was the intent.

(snj)