copies: separate moves via directory renames from explicit copies Currently the "copy" dict contains both explicit copies/moves made by a context and pending moves that need to happen because the other context moved the directory the file was in. For explicit copies, the dict stores a destination to source map, while for pending moves via directory renames, it stores a source to destination map. The merge code uses this fact in a non- obvious way to differentiate between these two cases. We make this explicit by storing these pending moves in a separate dict. The dict still has a source to destination map, but that is called out in the docstring.