[#3697] Error in configure if autoreconf needed for premium hooks

This ensures that configure will find the premium hooks if they exist,
or error if autoreconf needs to be run again to pick up the hooks'
additions to configure.

configure.ac

@@ -144,7 +144,10 @@ INCLUDED_HOOKS=
 PREMIUM=no
 PREMIUM_DIR=
 DISTCHECK_PREMIUM_CONFIGURE_FLAG=
-AC_DEFUN([AX_PREMIUM],[])
+AC_DEFUN([AX_PREMIUM],
+  [if test -f premium/config.m4; then
+    AC_MSG_ERROR([You appear to have added premium hooks after running autoreconf. Please run 'autoreconf -f -i' and then rerun this script.])
+  fi])
 # m4_sinclude includes the file if it exists at autoreconf time
 m4_sinclude(premium/config.m4)
 AC_SUBST(PREMIUM_DIR)