log: slowpath: only walk specified revision range during preparation
Even with --removed, it does not make sense to examine changesets outside
of the revision range that was specified by the user: the last phase only
yields a subset of (revs), preparation phase hence only has to examine
(revs) to fill correctly fncache.
# should print nothing
# should fail
abort: path 'b/x' is inside repo 'b'
abort: path 'b/x' is inside repo 'b'
# should fail
abort: path 'b/x' is inside repo 'b'
# should arguably print nothing
# should fail
abort: path 'b/a' is inside repo 'b'