convert: make filemap renames consistently override revision renames
When the source repository had a revision renaming "$new -> $old",
but the filemap a "$old -> $new" rename, the converted revision could
use either $new (deleting the file) or $old (keeping the file) when
getting the file data, depending on the lexicographical order of
those names. So the resulting revision would leave some files
untouched (as expected), but delete others arbitrarely.
Greg Ward, author of the original bfiles extension
Na'Tosha Bard of Unity Technologies
Fog Creek Software
Special thanks to the University of Toronto and the UCOSP program