polyMesh constructor re-searches for latest "faceZones" instead of using faces.instance()

If you have a mesh in a time directory with a faceZones in a previous time it will find this one. polyMesh constructor re-searches

    faceZones_
    (
        IOobject
        (
            "faceZones",
            time().findInstance
            (
                meshDir(),
                "faceZones",
                IOobject::READ_IF_PRESENT
            ),
            meshSubDir,
            *this,
            IOobject::READ_IF_PRESENT,
            IOobject::NO_WRITE
        ),
        *this
    ),

instead of using faces_.instance()

I think this is incorrect. mesh::readUpdate actually uses the facesInstance. I'll change it for now but open to suggestions. @mark @andy