b2/: simplified and corrected logic behind relop_redundant

We now generate the operator map algorithmically, which is a bit less
classy than solving the logical equations, but easier to get right.

Also renamed the somewhat vague "redundant" to "unreachable".

b2/test/hierrul

@@ -69,7 +69,7 @@ p = <predation> {
 EOF
 
 expect <<EOF
-h:6: warning: redundant condition
+h:6: warning: unreachable condition
 p=<predation> {
     mouse: { X=* }
     cat: { Y=* }