Merge pull request #359 from joakim-hove/build-on-OSX

Build on osx
Added (empty) test for function ecl_grid_cell_contains.
Added const qualifier to function.
Added test code to run loop through all get_ijk / get_xyz combinations.
Exported tetrahedron based volume calculation.
Added test for comparison of two different volume calculations.
Added more debug code for tetrahedron debugging.
Added coordinates for broken cell with wrong volume.
Create problematic cell.
Corrected tetrahedron decomposition so volume calculations work also with quirky cells; tetrahedron volume calculation is signed.
Cosmetic changes.
More debugging.
TRying alternative method for calculation central depth.
Added simple point_equal() function for absolute equality.
ADded lots of special case comparison for the corner points.
WHite space ???
Change point_equal() implementation to use memcmp().
Added function tetrahedron_fprintf().
Added k coordinate to cells; used to alternate tetraheder decomposition method when determining cell_contains().
Work In Progress - cell contains.