Religiously add back pmap_clear_modify() in vnode_pager_input until we figure
out why system performance isn't what we expect.
Submitted by: John Dyson (swap_pager) & David Greenman (vnode_pager)
improvements via the new routines pmap_qenter/pmap_qremove and pmap_kenter/
pmap_kremove. These routine allow fast mapping of pages for those
architectures that have "normal" MMUs. Also included is a fix to the
pageout daemon to properly check a queue end condition.
Submitted by: John Dyson
