context: make unknown/ignored/clean of cached status empty for equivalence Before this patch, "workingctx.status" caches the result of "dirstate.status" directly into "self._status". But "dirstate.status" is invoked with False "list*" arguments in normal "self._status" accessing route, and this makes "unknown"/"ignored"/"clean" of status empty. This may cause unexpected result of code paths internally accessing to them (accessors for external usage are already removed by previous patch). This patch makes "unknown"/"ignored"/"clean" of cached status empty for equivalence. Making them empty is executed only when at least one of "unknown", "ignored" or "clean" has files, for efficiency.