store: also return some information about the type of file `walk` found We start returning of 4th information in the `store.walk` return tuple: the type of the file. This will make it easier for caller to determine which kind of file they are looking at. This should especically help with the `upgrade-repo` code that has to do a lot of fragile index's file name comparison. Differential Revision: https://phab.mercurial-scm.org/D10315