`faceNodes` locations are incompatible with RBFMeshMotionSolver

[davidscn]

Related to #227. Using the adapter in an FSI simulation and selecting locations faceNodes; for the interface and the RBFMeshMotion (see also #241) leads to the following crash

#0  Foam::error::printStack(Foam::Ostream&) at ??:?
#1  Foam::sigSegv::sigHandler(int) at ??:?
#2  ? in /lib/x86_64-linux-gnu/libc.so.6
#3  Foam::IOobject::db() const at ??:?
#4  Foam::regIOobject::setUpToDate() at ??:?
#5  preciceAdapter::FSI::Displacement::read(double*, unsigned int) at ??:?
#6  preciceAdapter::Interface::readCouplingData() at ??:?
#7  preciceAdapter::Adapter::readCouplingData() at ??:?
#8  preciceAdapter::Adapter::configure() at ??:?
#9  Foam::functionObjects::preciceAdapterFunctionObject::read(Foam::dictionary const&) at ??:?
#10  Foam::functionObjects::preciceAdapterFunctionObject::preciceAdapterFunctionObject(Foam::word const&, Foam::Time const&, Foam::dictionary const&) at ??:?
#11  Foam::functionObject::adddictionaryConstructorToTable<Foam::functionObjects::preciceAdapterFunctionObject>::New(Foam::word const&, Foam::Time const&, Foam::dictionary const&) at ??:?
#12  Foam::functionObject::New(Foam::word const&, Foam::Time const&, Foam::dictionary const&) at ??:?
#13  Foam::functionObjectList::read() at ??:?
#14  Foam::Time::run() const at ??:?
#15  ? in /usr/lib/openfoam/openfoam2012/platforms/linux64GccDPInt32Opt/bin/pimpleFoam
#16  ? in /lib/x86_64-linux-gnu/libc.so.6
#17  __libc_start_main in /lib/x86_64-linux-gnu/libc.so.6
#18  ? in /usr/lib/openfoam/openfoam2012/platforms/linux64GccDPInt32Opt/bin/pimpleFoam
Segmentation fault (core dumped)

The RBFMeshMotion solver is only compatible using locations faceCenters; and we should try to safeguard against the behavior above.