pushbookmark: remove a <cond> and <val> or <other> construct We make the conditional explicit for the sake of readability.

pushbookmark: stop unrolling ancestors Now that ancestors has the same boolean property as a list, we can stop unrolling the set of ancestors. This should provide a significant speedup to this step as ancestor objects are smart and lazy.

ancestors: add a __nonzero__ method This allows using the object in a conditional the same way we can use list.

push: update bookmarks within the remote lock Updating bookmarks is part of the push. It should be done within the same lock as the other steps of the push.