blame: refactor porcelain output

blame: refactor porcelain output

This is in preparation for adding more porcelain output
options. The three changes are:

  1. emit_porcelain now receives the format option flags

  2. emit_one_suspect_detail takes an optional "repeat"
     parameter to suppress the "show only once" behavior

  3. The code for emitting porcelain suspect is factored
     into its own function for repeatability.

There should be no functional changes.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>