Use register_printf_specifier instead of deprecated register_printf_function, if available

configure.in

@@ -373,12 +373,18 @@ AC_TRY_RUN(
 [AC_MSG_RESULT([no])])
 
 AC_CHECK_FUNC(
-	[register_printf_function],
-	[AC_DEFINE(HAVE_PRINTF_HOOKS)],
-	[
-		AC_MSG_NOTICE([printf does not support custom format specifiers!])
-		vstr=true
-	]
+	[register_printf_specifier],
+	dnl new specifier functions with argument length
+	[AC_DEFINE(HAVE_PRINTF_SPECIFIER)],
+	[AC_CHECK_FUNC(
+		dnl deprecated function without argument length
+		[register_printf_function],
+		[AC_DEFINE(HAVE_PRINTF_FUNCTION)],
+		[
+			AC_MSG_NOTICE([printf does not support custom format specifiers!])
+			vstr=true
+		]
+	)]
 )
 
 if test x$vstr = xtrue; then