Show a renamed file's diff as the rename

A diff limited to the new name cannot see the old one, so the
diffstat's link for a renamed file, the commit page reached from that
file's log, and the file's rawdiff and patch all showed every line as
added. A path the old tree lacks is now diffed across the whole commit
with rename detection aimed at it alone, the way git blame looks for a
rename, so it is compared with the commit's deleted files and nothing
else. Doing it in cgit_diff_tree keeps the log's counts for that commit
in step with the page they link to.

The rawdiff and patch pages leave the diff to git's own output, so for
them that search finds the old name, and both names go into the limit
with rename detection on.

0 files changed, 0 insertions, 0 deletions