Added NSOpenGL manager.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code@4697 dfc29bdd-3216-0410-991c-e03cc46cb475
Prevent some precision troubles on some compilers when working with vector3d<s32>. Thx @AReichl for bugfix.


git-svn-id: svn://svn.code.sf.net/p/irrlicht/code@4698 dfc29bdd-3216-0410-991c-e03cc46cb475
Second try on fixing some rounding problem with vector3d<s32>.


git-svn-id: svn://svn.code.sf.net/p/irrlicht/code@4699 dfc29bdd-3216-0410-991c-e03cc46cb475