Have autoreconf fail if LT_INIT is not defined

If the LT_INIT macro is not available in a *.m4 file to be
found during the autoreconf run, it is impossible to build
a useful configure script.

Therefore, we blacklist the LT_INIT macro so when it appears
unexpanded in the configure script, autoreconf will report
the failure instead of silently creating a broken configure.

This is generally a good idea for any macro not shipped with
Automake or Autoconf.

configure.ac

@@ -73,7 +73,9 @@ esac
 AM_CONDITIONAL(OS_WIN32, test "$os_win32" = "true")
 AM_CONDITIONAL(OS_QNX, test "$os_qnx" = "true")
 
+m4_pattern_forbid([^LT_INIT])dnl
 LT_INIT([disable-static win32-dll pic-only])
+
 AC_CHECK_HEADERS([ \
     arpa/inet.h \
     byteswap.h \