simplified half space solid extrusion, fixed problems in triangle orientation

git-svn-id: http://ifcplusplus.googlecode.com/svn/trunk@32 06f6d6f3-f2e0-f239-6e86-ba6a5d17d3a5
git-svn-id: http://ifcplusplus.googlecode.com/svn/trunk@33 06f6d6f3-f2e0-f239-6e86-ba6a5d17d3a5
fixed mesh face orientation

git-svn-id: http://ifcplusplus.googlecode.com/svn/trunk@34 06f6d6f3-f2e0-f239-6e86-ba6a5d17d3a5