log: make -fr show complete history from the given revs
Right now it's very obtuse to show the history of a particular rev (hg log -r
'reverse(::foo)'). This changes the -f option to make it follow history for the
revs specified by -r.
The current -f -r behavior is to limit the result of -r to only the
commits that are ancestors of the current working copy. Changing this
is a bit of a BC break, but the old behavior is A) rare, B) easy to
emulate (& ::.), and C) currently undefined. The new behavior is
frequently requested enough that I think the change is worth it.