It used to be that diff-tree needed helper support to parse its
raw output to generate diffs, but these days git-diff-* family
produces the same output and the helper is not tied to diff-tree
anymore.  Drop "tree" from its name.

This commit is done separately to record just the rename and no
file content changes. The changes in the renamed files are recorded
in the next commit.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

Bundled with the changes in the unrenamed files.
Signed-off-by: NPetr Baudis <pasky@ucw.cz>