commit 3049946fa742b654afa9b24f8bc79f387f01aea9
Author: Brian <brian@yutani.localnet.net>
Date:   Wed Mar 14 12:52:53 2007 -0600

    clear the b->frontxrb->drawable field in xmesa_free_buffer(), see bug 7205

diff --git a/src/mesa/drivers/x11/xm_api.c b/src/mesa/drivers/x11/xm_api.c
index 776928d..cbbbd56 100644
--- a/src/mesa/drivers/x11/xm_api.c
+++ b/src/mesa/drivers/x11/xm_api.c
@@ -483,6 +483,12 @@ xmesa_free_buffer(XMesaBuffer buffer)
 
          /* mark as delete pending */
          fb->DeletePending = GL_TRUE;
+
+         /* Since the X window for the XMesaBuffer is going away, we don't
+          * want to dereference this pointer in the future.
+          */
+         b->frontxrb->drawable = 0;
+
          /* Unreference.  If count = zero we'll really delete the buffer */
          _mesa_unreference_framebuffer(&fb);