Merging phk's filedesc cleanup and lock pushdown.

[Jeff Roberson]

I am going to MFC phk's filedesc related work in the next few days.  This
is required if I am ever to merge the vfs smp changes.  I have a patch
available at:

http://www.chesapeake.net/~jroberson/fdesc.patch

I'd appreciate it if anyone who can would test this.  It has been running
on current for 3-4 months, depending on the bit, but there's always a
chance of a botched merge.

Thanks,
Jeff