Fix two bugs in r218670.
Fix two bugs in r218670.

Hold the vnode around the region where object lock is dropped, until
vnode lock is acquired.

Do not drop the vnode reference for a case when the object was
deallocated during unlock. Note that in this case, VV_TEXT is cleared
by vnode_pager_dealloc().

Reported and tested by:	pho
Reviewed by:	alc
MFC after:	3 days

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase