ENH: regIOobject store() now also registers the object

- previously the store() method just set the ownedByRegistry flag.
  Now ensure that it is indeed registered first.

- support register/store of tmp<> items.
  The tmp parameter is not cleared, but changed from PTR to CREF
  to allow further use.

  The implicit registration allows code simplification using the
  GeometricField::New factory method, for example.

  Old Code
  ========
      volScalarField* ptr = new volScalarField
      (
          IOobject
          (
              fieldName,
              mesh.time().timeName(),
              mesh,
              IOobject::NO_READ,
              IOobject::NO_WRITE,
              true  // Register
          ),
          mesh,
          dimless,
          zeroGradientFvPatchField<scalar>::typeName
      );
      ptr->store();

  New Code
  ========
      auto tptr = volScalarField::New
      (
          fieldName,
          mesh,
          dimless,
          zeroGradientFvPatchField<scalar>::typeName
      );
      regIOobject::store(tptr);

  or even
      regIOobject::store
      (
          volScalarField::New
          (
              fieldName,
              mesh,
              dimless,
              zeroGradientFvPatchField<scalar>::typeName
          )
      );