Fix crash in cgalpngtest_assign-tests
search(): fix crash bug and add additional feature

search(4,[1,2,3]) crashed OpenSCAD. Instead of crashing, one can now search vectors for matching elements.
In addition, search([[1,2]],[[0,1],[1,2],[2,3]]) will work and return [1].
Merge branch 'search_crashfix' of git://github.com/OskarLinde/openscad into OskarLinde-search_crashfix
#786 Added tests