building more tests for graph, now using the Graph*Request abstraction to avoid tempdir shenanigans.
test for extending an existing image lineage
also test that the deeper parts of the tree made it into git
test for new derived lineages, and bugfix for same.
clearly name tests that address publishing as such
more tests, now covering advancing multiple lineages and deriving them from each other.  more fixes for files coming along for the ride when they shouldn't.
drop now unused test helper methods that touched the filesystem.
change the default commit message format.
Merge remote-tracking branch 'origin/master'