fix more broken logic regarding commit stati
only look at most recent status when avoiding duplicates

i was treating the commit statuses as a Set to avoid duplicates,
but that ignores the fact that rebuilds should prepend a new status
so that more recent results, even if already in the history,
are moved to the front
don't github-reference PR in failure message: too noisy
no more sad kitty
add command NOLITTER! that deletes kitty's commit comments
don't set milestone if already set
Merge pull request #24 from adriaanm/cleanup

more commit status logic improvements