Use the original buffer-name as `base' in place of the

Use the original buffer-name as `base' in place of the
nondirectory part of the file name.
(uniquify-rationalize-file-buffer-names):
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.
(rename-buffer): Use the `newname' arg as base.
(create-file-buffer): Split the file name into base and dirname.