Split the `newbuffile' arg into `base' and `dirname'.
Reuse old uniquify-items to avoid recomputing their base&dirname.
(uniquify-buffer-file-name): Only return the directory part.
- (uniquify-rerationalize-w/o-cb): Don't bother reseting proposed names.
+ (uniquify-rerationalize-w/o-cb): Don't bother resetting proposed names.
(rename-buffer): Use the `newname' arg as base.
(create-file-buffer): Split the file name into base and dirname.