ENH: code reduction in PackedList, PackedBoolList (issue #751)

- eliminate iterators from PackedList since they were unused, had
  lower performance than direct access and added unneeded complexity.

- eliminate auto-vivify for the PackedList '[] operator.
  The set() method provides any required auto-vivification and
  removing this ability from the '[]' operator allows for a lower
  when accessing the values. Replaced the previous cascade of iterators
  with simpler reference class.

PackedBoolList:

- (temporarily) eliminate logic and addition operators since
  these contained partially unclear semantics.

- the new test() method tests the value of a single bit position and
  returns a bool without any ambiguity caused by the return type
  (like the get() method), nor the const/non-const access (like
  operator[] has). The name corresponds to what std::bitset uses.

- more consistent use of PackedBoolList test(), set(), unset() methods
  for fewer operation and clearer code. Eg,

      if (list.test(index)) ...    |  if (list[index]) ...
      if (!list.test(index)) ...   |  if (list[index] == 0u) ...
      list.set(index);             |  list[index] = 1u;
      list.unset(index);           |  list[index] = 0u;

- deleted the operator=(const labelUList&) and replaced with a setMany()
  method for more clarity about the intended operation and to avoid any
  potential inadvertent behaviour.

applications/utilities/mesh/manipulation/checkMesh/checkTools.C

@@ -309,7 +309,7 @@ void Foam::mergeAndWrite
     PackedBoolList isInSet(mesh.nCells());
     forAllConstIter(cellSet, set, iter)
     {
-        isInSet[iter.key()] = true;
+        isInSet.set(iter.key());
     }
 
 
@@ -329,8 +329,8 @@ void Foam::mergeAndWrite
     DynamicList<label> outsideFaces(3*set.size());
     for (label facei = 0; facei < mesh.nInternalFaces(); facei++)
     {
-        bool ownVal = isInSet[mesh.faceOwner()[facei]];
-        bool neiVal = isInSet[mesh.faceNeighbour()[facei]];
+        const bool ownVal = isInSet[mesh.faceOwner()[facei]];
+        const bool neiVal = isInSet[mesh.faceNeighbour()[facei]];
 
         if (ownVal != neiVal)
         {
@@ -349,7 +349,7 @@ void Foam::mergeAndWrite
             {
                 label facei = pp.start()+i;
 
-                bool neiVal = bndInSet[facei-mesh.nInternalFaces()];
+                const bool neiVal = bndInSet[facei-mesh.nInternalFaces()];
                 if (isInSet[fc[i]] && !neiVal)
                 {
                     outsideFaces.append(facei);