[patch] rw_try_wlock does not set recursive bit when recursing

Hi,
The following sequence of commands fails on line 4 with an assertion
that the lock is not currently held:

1: rw_wlock(&rw);
2: if ( rw_try_wlock(&rw) )
3:    rw_wunlock(&rw);
4: rw_wunlock(&rw);

This is because after line 3 is executed the rw lock is no longer
held. I tracked this bug down to _rw_try_wlock which correctly
increments rw_recurse, but does not set the RW_LOCK_RECURSED bit.
Without this bit the third line unlocks the lock and leaves it in a
unlocked state (when it should still be locked). Adding a line to set
this bit makes _rw_try_wlock match the code in _rw_wlock_hard.

I have attached a one line patch which fixes this problem on my 7.2
system, and looking over the CURRENT source it should also apply
cleanly (but I have not tested it on CURRENT). I have also attached
another (slightly longer) patch which fixes the problem as well as
adding an a extra assert. It is up to the FreeBSD developer to decide
which patch they prefer.

thanks
Andrew