Only use opengl debug groups if the LOVE_GRAPHICS_DEBUG environment variable is set to 1.

--HG--
branch : minor

src/modules/graphics/Graphics.cpp

@@ -28,6 +28,7 @@
 
 // C++
 #include <algorithm>
+#include <stdlib.h>
 
 namespace love
 {
@@ -35,6 +36,8 @@ namespace graphics
 {
 
 static bool gammaCorrect = false;
+static bool debugMode = false;
+static bool debugModeQueried = false;
 
 void setGammaCorrect(bool gammacorrect)
 {
@@ -80,6 +83,18 @@ Colorf unGammaCorrectColor(const Colorf &c)
 	return r;
 }
 
+bool isDebugEnabled()
+{
+	if (!debugModeQueried)
+	{
+		const char *debugenv = getenv("LOVE_GRAPHICS_DEBUG");
+		debugMode = debugenv != nullptr && debugenv[0] != '0';
+		debugModeQueried = true;
+	}
+
+	return debugMode;
+}
+
 love::Type Graphics::type("graphics", &Module::type);
 
 Shader::ShaderSource Graphics::defaultShaderCode[Shader::LANGUAGE_MAX_ENUM][2];