addremove: only query dirstate once per path
Previously the addremove code queried the dirstate 4 times per path. Now it
only does so once. On a large repo this brings addremove from 9.5 seconds
to 8.35 seconds (12%).
largefiles: don't crash when trying to find default dest for url without path
b32e55e6c3c7 introduced a crash when cloning a url without path - where
util.url().path would be None.
This None will now be handled as ''. clone will thus abort with 'repository /
not found' as before.