Workaround an xcb-dri2 bug.

xcb_dri2_connect_device_name generated by xcb-proto 1.6 is broken.  It
only works when the length of the driver name is a multiple of 4.
diff --git a/configure.ac b/configure.ac
index b510b51..f57e2bd 100644
--- a/configure.ac
+++ b/configure.ac
@@ -34,6 +34,11 @@
 	     [AC_MSG_ERROR([Can't find expat library. Please install expat.])])
 AC_SUBST(EXPAT_LIBS)
 
+# workaround a bug in xcb-dri2 generated by xcb-proto 1.6
+AC_CHECK_LIB(xcb-dri2, xcb_dri2_connect_alignment_pad, [],
+	     [AC_DEFINE([XCB_DRI2_CONNECT_DEVICE_NAME_BROKEN], [1],
+			[Define to 1 if xcb_dri2_connect_device_name is broken])])
+
 AC_CONFIG_FILES([wayland/wayland-server.pc
 		 wayland/wayland-client.pc
 		 Makefile