context.status: wipe deleted/unknown/ignored fields when reversed

It makes no sense to request reverse status (i.e. changes from the
working copy to its parent) and then look at the deleted, unknown or
ignored fields. If you do, you would get the result from the forward
status (changes from parent to the working copy). Instead of giving a
nonsensical answer to a nonsensical question, it seems a little saner
to return empty lists. It might be best if we could prevent the caller
accessing these lists, but it's doubtful it's worth the trouble.

mercurial/context.py

@@ -304,9 +304,12 b' class basectx(object):'
         r = ctx2._buildstatus(ctx1, r, match, listignored, listclean,
                               listunknown)
 
+        r = scmutil.status(*r)
         if reversed:
-            # reverse added and removed
-            r[1], r[2] = r[2], r[1]
+            # Reverse added and removed. Clear deleted, unknown and ignored as
+            # these make no sense to reverse.
+            r = scmutil.status(r.modified, r.removed, r.added, [], [], [],
+                               r.clean)
 
         if listsubrepos:
             for subpath, sub in scmutil.itersubrepos(ctx1, ctx2):
@@ -325,8 +328,7 b' class basectx(object):'
         for l in r:
             l.sort()
 
-        # we return a tuple to signify that this list isn't changing
-        return scmutil.status(*r)
+        return r
 
 
 def makememctx(repo, parents, text, user, date, branch, files, store,