bookmarks: properly invalidate volatile sets when writing bookmarks This corrects a regression introduced during the 3.7 cycle, but which went undetected due to the surviving-but-deprecated write() method on bmstore.

test-obsolete: update extension in test to actually work This hasn't been testing anything since partway through the 3.7 cycle due to unrelated refactoring. Sadly, the behavior it was trying to prevent reemerged in the codebase at that time. A fix is in the next patch, because proving that the fix was actually correct ended up being trickier than I expected.

bundle2: properly request phases during getbundle getbundle was requesting the "phase" namespace instead of the "phases" namespace, which led to the client still requesting the phases separately after getbundle finished.

rebase: handle successor targets (issue5198) When a parent has a successor (indicated by revprecursor in state), we need to use it.