- this can help if using std algorithms that return a const reference
  such as std::min() does.

- PtrDynList support for move append list:
  can be used to concatenate pointer lists into a single one

- include resize in PtrDynList squeezeNull as being a natural
  combination

- support sorting operations for pointer lists (PtrListOps)

- PtrList::release() method.

  Similar to autoPtr and unique_ptr and clearer in purpose than
  using set(i,nullptr)

- Construct from List of pointers, taking ownership.

  Useful when upgrading code. Eg,

     List<polyPatch*> oldList = ...;
     PtrList<polyPatch> newList(oldList);
     ...

BUG: incorrect resizing method names (PtrDynList) in previously unused code

- moves any nullptr to the end of the list where they can be
  eliminated in a second step with resize()

- can still test as a bool or use to 'peek' at the content.

    UPtrList::set(const label i, T* ptr);

No-op if the new pointer value is identical to the current content.
This avoid memory management issues.

- gets the pointer within the list.

- this eliminates a degree of ambiguity when resolving a read() method
  in inherited classes.

- resolve in favour of "inline explicit", which had marginally more
  uses and provides consistent prefixing for inline methods.

- catch (value)
- forward declarations for operator<<()
- non-const access to Reaction name()
- spurious return statement

- improve internal handling to permit deriving resizable containers
  (eg, PtrDynList).

- include '->' iterator dereferencing

- Only append/set non-const autoPtr references. This doesn't break
  existing code, but makes the intention more transparent.