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.
adding a
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3
a renamed from b:9a263dd772e0159ddfa70fb8a448bb6c7ec8c69f
% test with --rev
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3