git-blame: refactor code to emit "porcelain format" output
git-blame: refactor code to emit "porcelain format" output

Both the --porcelain and --incremental format shared the same output
format but implemented with two identical codepaths.  This merges them
into one shared function.

Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git