grep: extend functionality, add man page entry, add unit test. walkchangerevs now returns a two-tuple. Its behaviour is also extensively commented. The annotate command's getname function has been factored out to a new function, trimname, so it can be shared between annotate and grep. The behaviour of grep has been beefed up, so that it now performs a number of useful functions.

#!/bin/sh
hg init
echo This is file a1 > a
hg add a
hg commit -m "commit #0" -d "0 0"
ls
echo This is file b1 > b
hg add b
hg commit -m "commit #1" -d "0 0"
hg co 0
# B should disappear
ls