rebase: move actual rebase into a single transaction Previously, rebasing would open several transaction over the course of rebasing several commits. Opening a transaction can have notable overhead (like copying the dirstate) which can add up when rebasing many commits. This patch adds a single large transaction around the actual commit rebase operation, with a catch for intervention which serializes the current state if we need to drop back to the terminal for user intervention. Amazingly, almost all the tests seem to pass. On large repos with large working copies, this can speed up rebasing 7 commits by 25%. I'd expect the percentage to be a bit larger for rebasing even more commits. There are minor test changes because we're rolling back the entire transaction during unexpected exceptions instead of just stopping mid-rebase, so there's no more backup bundle. It also leave an unknown file in the working copy, since our clean up 'hg update' doesn't delete unknown files.

rebase: allow aborting if last-message.txt is missing Previously, if .hg/rebasestate existed but .hg/last-message.txt was missing, 'hg rebase --abort' would say there's no rebase in progress but 'hg checkout foo' would say 'abort: rebase in progress'. It turns out loading the collapse message will throw a "no rebase in progress" error if the file doesn't exist, even though .hg/rebasestate obviously indicates a rebase is in progress. The fix is to only throw an exception if we're trying to --continue, and to just eat the issues if we're doing --abort. This issue is exposed by us writing the rebase state earlier in the process. This will be used by later patches to ensure the user can appropriately 'hg rebase --abort' if there's a crash before the first the first commit has finished rebasing. Tests cover all of this. The only negative affect is we now require a hg rebase --abort in a very specific exception case, as shown in the test.

rebase: add storestatus support for transactions This let's the status writing logic support transactions. This will be useful in a later patch where we add a transaction around the entire rebase.

rebase: move storestatus onto rebaseruntime The rebaseruntime class already has the restorestatus function, so let's make it own the store status function too. This get's rid of a lot of unnecessary argument passing and will make a future patch cleaner that refactors storestatus to support transactions.