revset: make reverse() noop depending on ordering requirement (BC) Because smartset.reverse() may modify the underlying subset, it should be called only if the set can define the ordering. In the following example, 'a' and 'c' is the same object, so 'b.reverse()' would reverse 'a' unexpectedly. # '0:2 & reverse(all())' <filteredset <spanset- 0:2>, # a <filteredset # b <spanset- 0:2>, # c <spanset+ 0:9>>>