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.
% convert while testing all possible outputs
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
% check tags are in UTF-8
'221c3fdaf24df5f14c0a64c597581e2eacfb47bb branch\xc3\xa9e\n'
'7a40952c2db29cf00d9e31df3749e98d8a4bdcbf branch\xc3\xa9\n'