blame: fix unblamable and ignored lines in porcelain mode

The 'git-blame(1)' command allows users to ignore specific revisions via the '--ignore-rev ' and '--ignore-revs-file ' flags. These flags are often combined with the 'blame.markIgnoredLines' and 'blame.markUnblamableLines' config options. These config options prefix ignored and unblamable lines with a '?' and '*', respectively.

However, this option was never extended to the porcelain mode of 'git-blame(1)'. Since the documentation does not indicate this exclusion, it is a bug.

Fix this by ensuring porcelain mode also prints the markers and add tests to verify the behavior.

Closes #514 (closed)