[pygame] PATCH: add constants to allow setting OpenGL context and version

[Pascal Schuppli <pschuppli@xxxxxxx>]

I propose adding the patch below to the pygame code. It makes SDL's 
OpenGL-related constants  as defined by 
https://wiki.libsdl.org/SDL_GLprofile available in pygame when you 
compile pygame against SDL 2 (I diddn't check whether SDL 1 also 
provides these constants, so I put them inside an #if).

The patch is useful because it lets the programmer set the OpenGL 
context and version, which on some hardware (notably various Intel 
integrated graphics hardware) is necessary to get newer GLSL shader code 
to compile.

Here's an example of the code that the patch makes possible:

pygame.init()
pygame.display.gl_set_attribute(pygame.GL_CONTEXT_PROFILE_MASK, 
pygame.GL_CONTEXT_PROFILE_CORE)
pygame.display.gl_set_attribute(pygame.GL_CONTEXT_MAJOR_VERSION, 3)
pygame.display.gl_set_attribute(pygame.GL_CONTEXT_MINOR_VERSION, 3)

This solves issues like this one - 
https://gamedev.stackexchange.com/questions/126371/how-to-initialize-opengl-context-with-pygame-instead-of-glut.

The patch:

diff --git a/src_c/constants.c b/src_c/constants.c
index 3e10de95..e1096d9b 100644
--- a/src_c/constants.c
+++ b/src_c/constants.c
@@ -171,6 +171,15 @@ MODINIT_DEFINE(constants)
     DEC_CONST(GL_ACCUM_ALPHA_SIZE);

 #if IS_SDLv2
+    DEC_CONST(GL_CONTEXT_PROFILE_MASK);
+    DEC_CONST(GL_CONTEXT_PROFILE_CORE);
+    DEC_CONST(GL_CONTEXT_PROFILE_COMPATIBILITY);
+    DEC_CONST(GL_CONTEXT_PROFILE_ES);
+    DEC_CONST(GL_CONTEXT_MAJOR_VERSION);
+    DEC_CONST(GL_CONTEXT_MINOR_VERSION);
+#endif /* IS_SDL_v2 */
+
+#if IS_SDLv2
     DEC_CONST(BLENDMODE_NONE);
     DEC_CONST(BLENDMODE_BLEND);
     DEC_CONST(BLENDMODE_ADD);