[Bikeshed] sigacts locking

[John Baldwin]

As part of the locking for the proc structure, I needed to lock
the procsig and sigacts stuctures so that kill(), killpg(),
sigaction() and a few other system calls can be pulled out from
under Giant.  After talking with Peter some, I decided to
pull the sigacts structure out of the u-area and merge it with
the procsig structure under the sigacts name.  I then added a
mutex to each sigacts and added locking where appropriate.  With
this change, the aforementioned system calls are now MP safe
along with sendsig(), *signal(), cursig(), etc.  The patch for
all this is at http://www.FreeBSD.org/~jhb/patches/sigacts.patch
I would appreciate comments, review, etc. that people may have.
If all goes well I hope to get this into 5.1.  Thanks.

-- 

John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/