Add love.graphics.isSupported

Replaces love.graphics.hasPixelEffects and also does framebuffer support.

Also fixed 4 compiler warnings.

src/modules/graphics/opengl/wrap_Graphics.h

@@ -89,7 +89,7 @@ namespace opengl
 	int w_newScreenshot(lua_State * L);
 	int w_setRenderTarget(lua_State * L);
 	int w_setPixelEffect(lua_State * L);
-	int w_hasPixelEffects(lua_State * L);
+	int w_isSupported(lua_State * L);
 	int w_getGLSLVersion(lua_State * L);
 	int w_draw(lua_State * L);
 	int w_drawq(lua_State * L);