two fixes for current git

To clarify: that xBRZ commit is only noted here due to github lacking granularity (and me lacking a bit of patience to clean up that little mess).

So, the two commits should be rather obvious:
- for src/CMakeLists.txt: it seems FindGLEW.cmake was added upstream somewhere in 2012, which should be long enough and obviously glew32 is the name valid only for Windows
-  src/gl/shaders/gl_shader.cpp: don't know much about OpenGL, but current construct just throws GL_INVALID_OPERATION and going by http://www.arcsynthesis.org/gltut/Basics/Tut01%20Making%20Shaders.html that's what it's supposed to be