Make buffer age not glx specific

Buffer age is not a glx specific concept. xrender backend can have
buffer age too, if double buffering is used (required if we want to use
Present). So, make buffer age a generic concept in compton is required
for further backend improvements.

Moved buffer age based damage aggragation out of glx as well.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/render.h

@@ -27,7 +27,7 @@ void
 paint_one(session_t *ps, win *w, const region_t *reg_paint);
 
 void
-paint_all(session_t *ps, region_t *region, const region_t *region_real, win * const t);
+paint_all(session_t *ps, win * const t, bool ignore_damage);
 
 void free_picture(xcb_connection_t *c, xcb_render_picture_t *p);