Take 2.  Do a fairly mechanical reversion of the locking protocol
to that of revision 1.94.  Add a comment documenting my best guess
about the locking requirements in this subsystem.  Don't take locks
solely for the sake of stats counter increments; the locking around
the increment of ->ncs_pass2 and/or ->ncs_2passes caused a deadlock.
Defer fixing stats-keeping to allow this change to be easily backed
out of.
Simplify control flow

Removes a variable and compiler warnings in some cases.