Don't use RefCount int operators

Don't use RefCount int operators

, as those are going away.

The comment in QString/QByteArray::squeeze  about shared_null was updated as it
also affects other static data, such as that generated by QStringLiteral and
QByteArrayLiteral.

Change-Id: I26a757d29db62b1e3566a1f7c8d4030918ed8a89
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>