Panic on -CURRENT after LDT changes

[Tor Egge]

> Tor,
> I've updated the patch. Can you please redownload it and test/review:
> http://users.gufi.org/~rookie/works/patches/schedlock/ldt2.diff

Looking at the diff between the old ldt2.diff and the new ldt2.diff,
the change seems reasonable.

i386_ldt_grow() has another problem if multiple processes share a user LDT.
The old ldt is freed while still referenced by the CPUs.  This might cause
problems, e.g. with threaded linux binaries.

- Tor Egge