val: use the libjeffpc slab allocator API instead of libumem
val: use the libjeffpc slab allocator API instead of libumem

This makes the code more portable since now libjeffpc doesn't require
libumem.  (If libumem is present, the slab allocator API wraps it, so we
don't lose any functionality.)

Signed-off-by: Josef 'Jeff' Sipek <a620f141433c70aa9e43778305a6c68cbfadfb25@josefsipek.net>

jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc