rebase: move base calculation from rebasenode() to defineparents() We want to collect all calculation in one place.

largefiles: remove redundant checks for false modify/delete conflicts In a34a99181f36 (largefiles: don't show largefile/normal prompts if one side is unchanged, 2014-12-01), overridecalculateupdates() started checking for false modify/delete conflicts in large files and their standins. Then, in the very next changeset, 902554884335 (merge: before cd/dc prompt, check that changed side really changed, 2014-12-01), calculateupdates() itself started checking for false modify/delete conflicts in all files. Since "large files and their standins" is a subset of "all files", we can now drop the checks in overridecalculateupdates().

merge: make 'keep' message more descriptive Most merge action messages don't describe the action itself, they describe the reason the action was taken. The only exeption is the 'k' action, for which the message is just "keep" and instead there is a code comment folling it that says "remote unchanged". Let's move that comment into the merge action message.