commit some work-in-progress changes to make nfs client mp-safe to a branch,
so that they won't get lost.
	- sprinkle some locking
	- mark the filesystem, nfstimer callout, and kq kthread mp-safe
	- add assertions and comments
	- disable upgrade mount for now
	- some unrelated cosmetic changes
sync with head.
sync with head.
fix merge botches.
fix a merge botch.
fix a merge botch.
sync with head
wrap long lines.
revert the previous, which has been committed to the wrong branch.
sync with head
nfs_mount: re-enable MNT_UPDATE.  it's broken as it is in trunk.
lock vnode when calling VOP_GETATTR because there's no reasonable way for
an implementation of VOP_GETATTR to prevent the vnode from being revoked.
fix a merge botch.
remove sndlock.  it's superseded by nm_solock.
suggested by Andrew Doran.
sync with head.
debug printf and comments.  no functional changes.
sync with head.
sync with head
sync with head
fix merge botches