Add support for poll(2) on files. vop_nopoll() now returns POLLNVAL

if one of the new poll types is requested; hopefully this will not break
any existing code.  (This is done so that programs have a dependable
way of determining whether a filesystem supports the extended poll types
or not.)

The new poll types added are:

	POLLWRITE - file contents may have been modified
	POLLNLINK - file was linked, unlinked, or renamed
	POLLATTRIB - file's attributes may have been changed
	POLLEXTEND - file was extended

Note that the internal operation of poll() means that it is impossible
for two processes to reliably poll for the same event (this could
be fixed but may not be worth it), so it is not possible to rewrite
`tail -f' to use poll at this time.

0 files changed, 0 insertions, 0 deletions