Make sure all required m4 files are in place

configure.ac

@@ -7,6 +7,9 @@ AC_PREREQ([2.69])
 AC_INIT([libmtime], [1.2.0], [luis.kornblueh@mpimet.mpg.de])
 
 AC_CONFIG_MACRO_DIR([m4])
+dnl Make sure all required m4 files are in place:
+m4_pattern_forbid([^(A[SC]|D)X_])dnl
+m4_pattern_allow([^DX_(CLEAN(_|FILES)|(PDF|PS)_GOAL|SNIPPET_|V_)])dnl
 AC_CONFIG_AUX_DIR([config])
 AC_CONFIG_SRCDIR([include/mtime_calendar.h])
 AC_CONFIG_HEADERS([config/config.h])