[StGIT PATCH 0/6] New and improved DAG appliedness series

This took a while, but here it is. (Actually, I finished this about a week ago, but had no Internet connection so I couldn't send it.)

The series starts with basically the same DAG appliedness test as before, with the same known performance bug. Later on in the series, the mechanism is changed to one that doesn't have the bug. I kept the intermediate, slow state because the changesets read better that way, and because the new mechanism is more complicated than the old so it might be useful to be able to compare their output in case some bug turns up further down the road.

To test the performance, I used a script (which I've unfortunately misplaced) that (in the kernel repository) reset to one point 10000 commits in the past and one 5000 commits in the past, pushed a few patches at each spot, and then created 100 applied and 100 unapplied patches on top of upstream HEAD. This triggers the performance bug with the first algorithm since we have unapplied commits very far from HEAD.

Both algorithms are documented in the patches that introduce them.