demos: fix glxpixmap and call glXWaitGL before calling XCopyArea.
diff --git a/progs/xdemos/glxpixmap.c b/progs/xdemos/glxpixmap.c
index 9db4df2..e1abd22 100644
--- a/progs/xdemos/glxpixmap.c
+++ b/progs/xdemos/glxpixmap.c
@@ -178,6 +178,7 @@
    glColor3f( 0.0, 1.0, 1.0 );
    glRectf( -0.75, -0.75, 0.75, 0.75 );
    glFlush();
+   glXWaitGL();
 
    XMapWindow( dpy, win );