largefiles: drop partial support for not having a user cache 971c55ce03b8 introduced support for not having a "global" user cache. In the rare cases where the environment didn't provide the location of the current home directory, the usercachepath function could return None. That functionality has since bitrotten and several code paths did not correctly check for usercachepath returning None: $ HOME= XDG_CACHE_HOME= hg up --config extensions.largefiles= getting changed largefiles abort: unknown largefiles usercache location Dropping the partial support for it is thus not really a backward compatibility breaking change. Thus: consistently fail early if the usercache location is unknown. It is relevant to be able to control where the largefiles are stored and how they propagate, but that should probably be done differently. The dysfunctional code just gets in the way.