Syncronize filesystems to disk when suspending. Each mountpoint's vnodes

Syncronize filesystems to disk when suspending.  Each mountpoint's vnodes
are pushed to disk.  Dangling vnodes (unlinked files still in use) and
vnodes undergoing change by long-running syscalls are identified -- and
such filesystems are marked dirty on-disk while we are suspended (in case
power is lost, a fsck will be required).  Filesystems without dangling or
busy vnodes are marked clean, resulting in faster boots following
"battery died" circumstances.
Tested by numerous developers, thanks for the feedback.