STYLE: use 'is_sorted()' instead of 'sorted()' for readers, Pair, ...

- avoids naming ambiguity between querying sorted state vs returning a
  sorted list (for example)

ENH: add 'good()' method to a few more classes

applications/utilities/surface/surfaceClean/collapseEdge.C

@@ -68,7 +68,7 @@ static triSurface pack
         f[1] = pointMap[f[1]];
         f[2] = pointMap[f[2]];
 
-        if (f.valid())
+        if (f.good())
         {
             newTriangles[nNewTris++] = f;
         }