Merge branch 'hn/highlight-sideband-keywords'

Lines that begin with a certain keyword that come over the wire, as
well as lines that consist only of one of these keywords, ought to
be painted in color for easier eyeballing, but the latter was
broken ever since the feature was introduced in 2.19, which has
been corrected.

* hn/highlight-sideband-keywords:
  sideband: color lines with keyword only