bundle: refactor changegroup prune to be its own function Moving the prune function to be a non-nested function allows extensions to control which revisions are allowed in the changegroup. For example, in my shallow repo extension I want to prevent filelogs from being added to the bundle. This also allows an extension to use a filelog implementation that doesn't have revlog.linkrev implemented.

filectx: refactor filectx.rev() to use filectx._changeid The code in filectx.rev() was identical to filectx._changeid. Fixing this allows alternative filectx implementations to only override _changeid.

util: add an optional timestamp parameter to makedate This will be used by the upcoming shelve extension.

util: rename ct variable in makedate to timestamp