archive: delay extraction of file revisions
This allows us to look only at the filelogs we're interested in,
providing a nice speedup if we're archiving only part of a repository.
adding dir/bar
adding foo
dir/bar
foo
adding dir/bar_2
adding foo_2
dir/bar_2
foo_2
adding a
adding c
adding b
adding d
removing a
removing c
recording removal of a as rename to b (100% similar)