Detect scroll buttons which are exposed as BTN_FORWARD and BTN_BACK by the
kernel. Once detected by synaptics, scroll button repeat is working again.

--- xserver-xorg-input-synaptics-1.6.2.orig/src/eventcomm.c
+++ xserver-xorg-input-synaptics-1.6.2/src/eventcomm.c
@@ -446,7 +446,8 @@
 
         if ((TEST_BIT(BTN_0, keybits) != 0) ||
             (TEST_BIT(BTN_1, keybits) != 0) ||
-            (TEST_BIT(BTN_2, keybits) != 0) || (TEST_BIT(BTN_3, keybits) != 0))
+            (TEST_BIT(BTN_2, keybits) != 0) || (TEST_BIT(BTN_3, keybits) != 0) ||
+            (TEST_BIT(BTN_FORWARD, keybits) != 0) || (TEST_BIT(BTN_BACK, keybits) != 0))
             priv->has_scrollbuttons = 1;
     }