Fix bug #345. The last hit for a file might have been before the last window, so we can't clear copies. To reduce the load, we only store real copy entries instead of storing hashes for every revision.

changeset:   0:9426b370c206
tag:         tip
user:        My Name <myname@example.com>
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     commit-1