push: gather all bookmark decisions together The discovery phases for bookmarks now use the list of explicitly pushed bookmarks to do addition, removal and overwriting. Tests are impacted because this reduces the amount of listkeys calls issued, removes some duplicated messages and improves the accuracy of some messages.

push: prepare the issue of multiple kinds of messages To gather all the bookmark pushing actions together, we need code performing those actions to be ready for them. We need to be able to produce different messages for different actions.