Make sure we use the correct luac version when using contribs

configure.ac

@@ -1524,6 +1524,9 @@ then
   AS_IF([test "${LUAC}" = "false"], [
     AC_MSG_ERROR([Could not find the LUA byte compiler.])
   ])
+  AS_IF([test -f ${CONTRIB_DIR}/lib/liblua.a -a `echo|${LUAC} -o - -|od -j 8 -N 2 -t x2|head -n 1|cut -d' ' -f2` != 0404], [
+    AC_MSG_ERROR([You need 32-bits luac when using using lua from contrib.])
+  ])
 fi
 AM_CONDITIONAL(BUILD_LUA, [test "${have_lua}" = "yes"])