[cogl] Move debugging to a configure-time switch

Currently, COGL depends on defining debug symbols by manually
modifying the source code. When it's done, it will forcefully
print stuff to the console.

Since COGL has also a pretty, runtime selectable debugging API
we might as well switch everything to it.

In order for this to happen, configure needs a new:

        --enable-cogl-debug

command line switch; this will enable COGL debugging, the
CoglHandle debugging and will also turn on the error checking
for each GL operation.

The default setting for the COGL debug defines is off, since
it slows down the GL operations; enabling it for a particular
debug build is trivial, though.

clutter/cogl/common/cogl-debug.c

@@ -38,7 +38,8 @@ static const GDebugKey cogl_debug_keys[] = {
   { "offscreen", COGL_DEBUG_OFFSCREEN },
   { "draw", COGL_DEBUG_DRAW },
   { "pango", COGL_DEBUG_PANGO },
-  { "rectangles", COGL_DEBUG_RECTANGLES }
+  { "rectangles", COGL_DEBUG_RECTANGLES },
+  { "handle", COGL_DEBUG_HANDLE }
 };
 
 static const gint n_cogl_debug_keys = G_N_ELEMENTS (cogl_debug_keys);