mesa: pass context parameter to gl_renderbuffer::Delete()

We sometimes need a rendering context when deleting renderbuffers.
Pass it explicitly instead of trying to grab a current context
(which might be NULL).  The next patch will make use of this.

Note: this is a candidate for the stable branches.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>

src/mesa/main/shared.c

@@ -253,10 +253,11 @@ delete_framebuffer_cb(GLuint id, void *data, void *userData)
 static void
 delete_renderbuffer_cb(GLuint id, void *data, void *userData)
 {
+   struct gl_context *ctx = (struct gl_context *) userData;
    struct gl_renderbuffer *rb = (struct gl_renderbuffer *) data;
    rb->RefCount = 0;  /* see comment for FBOs above */
    if (rb->Delete)
-      rb->Delete(rb);
+      rb->Delete(ctx, rb);
 }