namespaces: copy implementation to new namespace object

namespaces: add a namespace object Currently, we use a dictionary object to store the namespace properties. This is python so let's use an object. This will allow us to be more flexible in our method signatures in the future.

localrepo: use vfs.reljoin rather than os.path.join in the localrepository class The removes the last remaining usage of os.path.join inside teh localrepository class.

largefiles: drop a redundant check for patterns when removing without --after This is in the way of passing a matcher to removelargefiles(). This method is called in exactly two places- first in overrides.addremove() (but only if the pattern list passed to it is not empty), and second in the commands.remove() override. But since the latter calls commands.remove() first, which also does this check, it isn't needed here.