Add grep command. It currently searches all revs of every matching file. I'll change this soon so that it can still do this, but it will not be the default behaviour. Many options are unimplemented. There's only one output mode. Binary files are not handled yet.

\.elc$
\.orig$
\.rej$
~$
\.so$
\.pyc$
\.swp$
\.prof$
^tests/.*\.err$
^build/
^dist/
^doc/.*\.[0-9](\.(x|ht)ml)?$
^MANIFEST$
^\.pc/
^patches/
^mercurial/__version__.py$