Adds App::MarkFile::check_collisions(). Right now this just bails if
something would be weird. An option to solve interactively is probably
a good idea, but for now this will at least prevent the obvious
foot-shooting case.
Of course it should probably also list the overlapping source paths...
- Moves more stuff into App::MarkFiles.
- Renames each() to each_path() and simplifies the interface from
handing a hashref to the callback to just giving it a path string.
- Adds mark-remove(1) and renames App::MarkFiles::unmark() to remove()