rebase: fix --collapse when a file was added then removed When a series of commits first adds a file and then removes it, hg rebase --collapse prompts whether to keep the file or delete it. This is due to it reusing the branch merge code. In a noninteractive terminal it defaults to keeping the file, which results in a collapsed commit that is has a file that should be deleted. This bug resulted in developers accidentally commiting unintentional changes to our repo twice today, so it's fairly important to get fixed. This change allows rebase --collapse to tell the merge code to accept the latest version every time without prompting. Adds a test as well.