[issue1020] Allocate lwkt threads with objcache

[Matthew Dillon]

:New submission from Nicolas Thery <nthery at gmail.com>:
:
:This patch uses an objcache instead of a custom per-CPU cache and a zone to=20
:allocate and free struct thread instances.
:
:I'll commit it in a couple of days if nobody objects.

    I haven't tested it but it looks like a nice cleanup.

						-Matt