status: do not reverse deleted and unknown

When reversing a status, trading "added" and "removed" make sense.
Reversing "deleted" and "unknown" does not. We stop doing it.

The reversing is documented in place for the poor soul not even able to remember
the index of all status elements by heart.

mercurial/context.py

@@ -320,7 +320,8 b' class basectx(object):'
                              listunknown)
 
         if reversed:
-            r[1], r[2], r[3], r[4] = r[2], r[1], r[4], r[3]
+            # reverse added and removed
+            r[1], r[2] = r[2], r[1]
 
         if listsubrepos:
             for subpath, sub in scmutil.itersubrepos(ctx1, ctx2):