Add free function vertexNeighbours() and test.
Fix BOOST_TEST_MODULE macro.
Add orderCounterClockwise() and test.
Minor fixes for FaceCellsProxy::operator().

Fixes are:
 - Made the method const.
 - Corrected argument name cell_index -> face_index.
Use GridHelpers in implementation of vertexNeighbours().
Whitespace: tabs to spaces.
Rename vertexNeighbours() -> cellNeighboursAcrossVertices().
Replace M_PI with boost usage.
Fix comment referencing renamed function.
Fix more whitespace tab->space issues.
Simplify formula with atan2().
Use proper way to access pi() from boost::math.
Merge pull request #685 from atgeirr/vertex-neighbours

Add free function vertexNeighbours() and test.
PVT properties: allow them to be temperature dependent

Note that this patch does not introduce any real temperature
dependence but only changes the APIs for the viscosity and for the
density related methods. Note that I also don't like the fact that
this requires so many changes to so many files, but with the current
design of the property classes I cannot see a way to avoid this...
Merge pull request #688 from andlaus/temperature_dependent_PVT

PVT properties: allow them to be temperature dependent
Silence unused argument warning.
Merge pull request #694 from atgeirr/silence-warning

Silence unused argument warning.