dispatch: move command dispatching into its own module
- move command dispatching functions from commands and cmdutil to dispatch
- change findcmd to take a table argument
- remove circular import of commands in cmdutil
- privatize helper functions in dispatch
adding dir/bar
adding foo
dir/bar
foo
adding dir/bar_2
adding foo_2
dir/bar_2
foo_2
adding a
adding c
adding b
adding d
removing a
removing c
recording removal of a as rename to b (100% similar)