ENH: cleanup autoPtr class (issue #639)

Improve alignment of its behaviour with std::unique_ptr

  - element_type typedef
  - release() method - identical to ptr() method
  - get() method to get the pointer without checking and without releasing it.
  - operator*() for dereferencing

Method name changes

  - renamed rawPtr() to get()
  - renamed rawRef() to ref(), removed unused const version.

Removed methods/operators

  - assignment from a raw pointer was deleted (was rarely used).
    Can be convenient, but uncontrolled and potentially unsafe.
    Do allow assignment from a literal nullptr though, since this
    can never leak (and also corresponds to the unique_ptr API).

Additional methods

  - clone() method: forwards to the clone() method of the underlying
    data object with argument forwarding.

  - reset(autoPtr&&) as an alternative to operator=(autoPtr&&)

STYLE: avoid implicit conversion from autoPtr to object type in many places

- existing implementation has the following:

     operator const T&() const { return operator*(); }

  which means that the following code works:

       autoPtr<mapPolyMesh> map = ...;
       updateMesh(*map);    // OK: explicit dereferencing
       updateMesh(map());   // OK: explicit dereferencing
       updateMesh(map);     // OK: implicit dereferencing

  for clarity it may preferable to avoid the implicit dereferencing

- prefer operator* to operator() when deferenced a return value
  so it is clearer that a pointer is involve and not a function call
  etc    Eg,   return *meshPtr_;  vs.  return meshPtr_();

applications/utilities/mesh/advanced/selectCells/selectCells.C

@@ -416,20 +416,14 @@ int main(int argc, char *argv[])
     );
 
 
-    // Surface
-    autoPtr<triSurface> surf(nullptr);
-    // Search engine on surface.
-    autoPtr<triSurfaceSearch> querySurf(nullptr);
-
     if (useSurface)
     {
-        surf.reset(new triSurface(surfName));
+        triSurface surf(surfName);
 
         // Dump some stats
-        surf().writeStats(Info);
+        surf.writeStats(Info);
 
-        // Search engine on surface.
-        querySurf.reset(new triSurfaceSearch(surf));
+        triSurfaceSearch querySurf(surf);
 
         // Set cellType[celli] according to relation to surface
         cutBySurface