merge: pass verbosity flag down to merge-recursive

This makes "git merge --quiet" really quiet when we call into merge-recursive. Note that we can't just pass our flag down as-is; the two parts of the code use different scales. We center at "0" as normal for git-merge (with "--quiet" giving a negative value), but merge-recursive uses "2" as its center. This patch passes a negative value to merge-recursive rather than "1", though, as otherwise the user would have to use "-qqq" to squelch all messages (but the downside is that the user cannot distinguish between levels 0-2 if without resorting to the GIT_MERGE_VERBOSITY variable). We may want to review and renormalize the message severities in merge-recursive, but that does not have to happen now. This is at least in improvement in the sense that we are respecting "--quiet" at all. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>