Log message printout cleanups (#2)

Log message printout cleanups (#2)

Here's a further patch on top of the previous one with cosmetic
improvements (no "real" code changes, just trivial updates):

 - it gets the "---" before a diffstat right, including for the combined
   merge case. Righ now the logic is that we always use "---" when we have
   a diffstat, and an empty line otherwise. That's how I visually prefer
   it, but hey, it can be tweaked later.

 - I made "diff --cc/combined" add the "---/+++" header lines too. The
   thing won't be mistaken for a valid diff, since the "@@" lines have too
   many "@" characters (three or more), but it just makes it visually
   match a real diff, which at least to me makes a big difference in
   readability. Without them, it just looks very "wrong".

   I guess I should have taken the filename from each individual entry
   (and had one "---" file per parent), but I didn't even bother to try to
   see how that works, so this was the simple thing.

With this, doing a

	git log --cc --patch-with-stat

looks quite readable, I think. The only nagging issue - as far as I'm
concerned - is that diffstats for merges are pretty questionable the way
they are done now. I suspect it would be better to just have the _first_
diffstat, and always make the merge diffstat be the one for "result
against first parent".

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