The earlier behaviour of grep was quite counter intuitive as it searches
history by default. It throws up matches from files which have been
deleted and commited out. This patch handles only the default behaviour
by iterating on the files being tracked by the workingctx are
not marked for removal
Edit1: remove displaying 'None' as the revision number in the output
Edit2: set the node of wdir instead of passing as suggested by Sean and Yuja