ERT-480: Added method matrix_det2() and improved testing of matrix_det4().
ERT-480: Added function for calculating the crossing of two lines.
ERT-480: Added several small methods to the point structure.
ERT-480: Changed the tetrahedron decomposition in ecl_grid + using tetrahedron based code for cell volumes; retaining sign of tetrahedron volume calculations.
ERT-480: Minor compile fix.
ERT-480: Minor test/compile fixes.
Minor test fixup
Merge pull request #404 from joakim-hove/ERT-480-submit

Ert 480 submit