git --diff: fix traceback when getting mode change
- use the manifest instead of the mode in the working dir
if the diff is against two revisions
- add a testcase
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)