verify: move manifest verification to its own function
This makes verify more modular, making it easier for extensions to extend.
%include map-cmdline.default
changeset = '{cset}{branches}{bookmarks}{tags}{lphase}{parents}{user}{ldate}{summary}\n'
changeset_verbose = '{cset}{branches}{bookmarks}{tags}{lphase}{parents}{user}{ldate}{lfiles}{lfile_copies_switch}{description}\n'