Fix deadlock introduced in 1.73 (Jan 1998).  The paging-in-progress count on a vnode-backed object must be incremented *after* obtaining the vnode lock.  If it is bumped before obtaining the vnode lock we can deadlock against vtruncbuf().
Fix deadlock introduced in 1.73 (Jan 1998).  The paging-in-progress count
on a vnode-backed object must be incremented *after* obtaining the vnode
lock.  If it is bumped before obtaining the vnode lock we can deadlock
against vtruncbuf().

Submitted by:	peter, ps
MFC after:	3 days

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