Fix vbo mesh draw instanced example

This change allows the example to run using either the fixed function pipeline / OpenGL 2.0 + GLSL 1.20 or OpenGL 3.2 + GLSL 150, depending on an #ifdef set in testApp.h

By default, this example will run using the fixed function GL renderer. (OpenGL 2.0)

Bonus: Two shader pairs (one GLSL 1.20 one GLSL 150 ) allow you to compare syntax differences between the two shader language versions.

Fixes #2427