merge: include ancestor node in merge actions

merge with stable

repoview: use _gethiddenblockers in computehidden No functionality has changed, since we've only extracted the code into its own function. Now extensions can wrap _gethiddenblockers to provide their own blocker without polluting bookmarks or local tags.

repoview: add _gethiddenblockers method This is a standalone function that will provide the ability for extensions to wrap.