Fix running on Linux / Intel Mesa drivers

* Explicitly request a GL 3.2 context
* Enable 'experimental' extensions on glew (This appears necessary to get glew to work with explictly set GL versions)

Engine/source/gfx/gl/sdl/gfxGLDevice.sdl.cpp

@@ -83,6 +83,10 @@ void GFXGLDevice::enumerateAdapters( Vector<GFXAdapter*> &adapterList )
     );
 
    SDL_ClearError();
+   SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
+   SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);
+   SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
+
    SDL_GLContext tempContext = SDL_GL_CreateContext( tempWindow );
    if( !tempContext )
    {

Engine/source/gfx/gl/tGL/tGL.cpp

@@ -29,6 +29,7 @@ namespace GL
 {
    void gglPerformBinds()
    {
+      glewExperimental = GL_TRUE;
       GLenum err = glewInit();
       AssertFatal(GLEW_OK == err, avar("Error: %s\n", glewGetErrorString(err)) );
    }

Engine/source/platformSDL/sdlPlatformGL.cpp

@@ -13,18 +13,16 @@ namespace PlatformGL
            return;
 
        inited = true;
-       const U32 majorOGL = 4;
+       const U32 majorOGL = 3;
        const U32 minorOGL = 2;
        U32 debugFlag = 0;
 #ifdef TORQUE_DEBUG
        debugFlag |= SDL_GL_CONTEXT_DEBUG_FLAG;
 #endif
 
-#if 0  // cause problem with glew, no extension load
        SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, majorOGL);
        SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, minorOGL);
        SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
-#endif
        SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, debugFlag);
 
        SDL_ClearError();