Added support for fullscreen window manager on linux. Patch provided by Deve.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@4918 dfc29bdd-3216-0410-991c-e03cc46cb475
Fixed issues with setViewPort method under OpenGL. (reported by anontypist)

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@4919 dfc29bdd-3216-0410-991c-e03cc46cb475