New bits in tip

[Matt Mackall]

Permission handling is in tip. It only tracks executable status and
it's not as smart as what TAH suggested yet, but it works.

Also, there's update -C and update -m. -C forces an update, clobbering
local files, -m allows a merge when mercurial thinks there are conflicts.

As permissions adds yet another dimension to merge, there might be
some new bugs lurking there.

And the usual bunch of other bugfixes and cleanups.

If someone (Jake?) would like to go and touch up the docstrings in
commands.py with the full documentation from doc/ and somehow figure
out a way to keep them in sync, that'd be great.

-- 
Mathematics is the supreme nostalgia of our time.