Fix missing include directory when building tests

This patch is currently required for all versions of mx
Upstream-Status: Submitted @ https://github.com/clutter-project/mx/issues/82
Signed-off-by: Tomas Frydrych <tomas@sleepfive.com>
--
Index: git/tests/Makefile.am
===================================================================
--- git.orig/tests/Makefile.am	2013-05-08 15:18:56.918596425 +0100
+++ git/tests/Makefile.am	2013-05-08 15:23:26.864781401 +0100
@@ -10,7 +10,8 @@
 
 INCLUDES = \
 	-I$(top_srcdir) \
-	-I$(top_builddir)
+	-I$(top_builddir)\
+	-I$(top_builddir)/mx
 
 noinst_PROGRAMS = 			\
 	test-deform-texture		\