py: error out if a "skip" character was given with non-dict to util.dirs() util.dirs() keeps track of the directories in its input collection. If a "skip" character is given to it, it will assume the input is a dirstate map and it will skip entries that are in the given "skip" state. I think this is used only for skipping removed entries ("r") in the dirtate. The C implementation of util.dirs() errors out if it was given a skip character and a non-dict was passed. The pure implementation simply ignored the request skip state. Let's make it easier to discover bugs here by erroring out in the pure implementation too. Let's also switch to checking for the dict-ness, to make the C implementation (since that's clearly been sufficient for many years). This last change makes test-issue660.t pass on py3 in pure mode, since the old check was for existence of iteritems(), which doesn't exist on py3. Differential Revision: https://phab.mercurial-scm.org/D6669