Merge pull request #1 from rodrigois/master

Few changes to support filter of degenerate triangles
modified gitignore to ignore Makefile
Merge pull request #2 from rodrigois/master

Reversed faces are reversed before being added
Merge pull request #3 from rodrigois/master

Fixed small bug
commented out flip faces warning because it was winding me up
Added to Nef_polyhedron_test to highlight the fact that one of the CGAL assertion errors seems to cause ruby to crash
Investigating split method with degen volumes
Merge pull request #4 from rodrigois/master

Minor additions related to computing the area of polygon sets
Regularization method added to Nef class
Merge branch 'master' of github.com:noelwarr/rgal
implemented off_to_nef_3 in Nef constructor to avoid self intersecting polyhedra
removed show method from one of the tests so that it would run smoothly on server
Applied some checking to polygons before inwards offsetting (Contributed by Rodrigo).  Also changed compilation to make use of two CPUs
added a few more Nef functions such as closure and interior
added functionality to split and new methods in Nef_polyhedron that regularizes things and avoids non valid Nefs
small chage to structuring of nefs
Small change to the Nef.build_cube method allowing for two points to be specified instead of taking the first to be the origin by default
Nef test was not working from test all because it relied on the DATA constant.  Small hack to fix that.
Slight change to how Nef.build_polygon works.  Now takes an array of points instead of an array of arrays.
removed a minkowski benchtest accidentally left in last commit