git-diff/git-apply: make diff output a bit friendlier to GNU patch (part 2)

git-diff/git-apply: make diff output a bit friendlier to GNU patch (part 2)

Somebody was wondering on #git channel why a git generated diff
does not apply with GNU patch when the filename contains a SP.
It is because GNU patch expects to find TAB (and trailing timestamp)
on ---/+++ (old_name and new_name) lines after the filenames.

The "diff --git" output format was carefully designed to be
compatible with GNU patch where it can, but whitespace
characters were always a pain.

This adds an extra TAB (but not trailing timestamp) to old_name
and new_name lines of git-diff output when the filename has a SP
in it.  An earlier patch updated git-apply to prepare for this.

Signed-off-by: Junio C Hamano <junkio@cox.net>