Fix 'filter --shell' command not being invoked for commits
The shell command provided to filter --shell
is never invoked for
commits because the attributes
set it passes to data_traverse()
is
unconditionally empty, so data_traverse()
never even attempts to apply
the filter to any fields of the commit.
This was broken by 2014-04-17T07:07:49-04:00!esr@thyrsus.com, which
also broke filter --dedos
due to the same cause, however, --dedos
was fixed by 2014-04-17T07:14:25-04:00!esr@thyrsus.com, but --shell
never was, so fix it now.