Changes to pull.

- ignore "d" log entries if file has not been deleted on sources
- suppress "locally modified" conflicts when the local file
	and the remote file are identical.
- make conflict messages begin with "!" verb

The first change is intended to make things like the db snafu
last week less painful.

The second change makes submitting patches nicer.  Assuming the
patch is accepted verbatim, pulling will not complain about the
files that you patched and got changed on sources.

The second change also makes it possible to copy files from sources
directly instead of using pull -s.  That is, you can do:

	% pull
	! sys/src/libc/port/lock.c locally modified; will not update
	% diff /sys/src/libc/port/lock.c /n/sources/plan9/sys/src/libc/port/lock.c
	... (decide changes are worth throwing away)
	% cp /n/sources/plan9/sys/src/libc/port/lock.c .
	% pull

This also helps if you submit a patch and the files get tweaked
a little on the way to sources.