Added headunit to autotools files

configure.ac

@@ -28,6 +28,8 @@ AC_CHECK_LIB([glib-2.0], [main], [],
     [AC_MSG_ERROR([glib-2.0 is required for profanity])])
 AC_CHECK_LIB([notify], [main], [], 
     [AC_MSG_NOTICE([libnotify not found])])
+AC_CHECK_LIB([headunit], [main], [], 
+    [AC_MSG_NOTICE([headunit not found, will not be able to run tests])])
 
 # Checks for header files.
 AC_CHECK_HEADERS([stdlib.h string.h])