Update JoglGL.java

Partial fix of the issue 205:
https://github.com/void256/nifty-gui/issues/205
Update JoglRenderImage.java

Uses GLUgl2 instead of GLU to benefit of a full implementation
Update Tools.java

Uses GLU.createGLU(GL).
Update JoglCoreGL.java

Same mistake than in JoglGL...
Merge pull request #207 from gouessej/patch-1

Patch 1: fix of the issue 205 + better GLU instanciation