convert: look up copies in getchanges instead of getcommit
svn: defer path expansion until getchanges to reduce latency, as well as memory
usage when converting incrementally.
Is there an error message when trying to diff non-existing files?
found: No such file or directory
not: No such file or directory
Is there an error message when trying to add non-existing files?
found: No such file or directory
not: No such file or directory