r3540: added testing of SMBntcancel in the open/open/close mux

r3540: added testing of SMBntcancel in the open/open/close mux
testing. Interestingly, w2k3 does not allow the cancel of an
outstanding async open request, whereas it does allow the cancel of an
outstanding async lock request. To support this I have changed the
pvfs_wait interface to provide a enum on why the event is happening,
so the callback can decide what to do.
(This used to be commit f23d6a28008a13588cde24b5012ec21e488ac47a)