Add IVideoDriver::getAmbientLight function so shader callbacks can access global ambient light easier.


git-svn-id: svn://svn.code.sf.net/p/irrlicht/code@4941 dfc29bdd-3216-0410-991c-e03cc46cb475
Add global ambient light to gles2 fixed function simulation shaders.


git-svn-id: svn://svn.code.sf.net/p/irrlicht/code@4942 dfc29bdd-3216-0410-991c-e03cc46cb475