Fix autorename feature so that it calls suggestName() correctly.

It was moving files into other directories unexpectedly.
Based on toddrme's patch, but also handles other cases (same partition
vs different partition), and a fix for non-interactive mode in order to
test this feature from a unittest (trunk only, needs new API)

BUG: 256650
FIXED-IN: 4.6.1
(cherry picked from commit fa1e90f4ba42f1267c12d1a28de3acf9fcbebb01)