give libusb-1.0+ libftdi users a tip about --with-async-mode

git-svn-id: https://urjtag.svn.sourceforge.net/svnroot/urjtag/trunk@1796 b68d4a1b-bc3d-0410-92ed-d4ac073336b7

urjtag/ChangeLog

@@ -2,6 +2,9 @@
 
   * src/tap/usbconn/libftdi.c (usbconn_ftdi_flush): Fix gcc printf warning.
 
+  * configure.ac: Have the libftdi + libusb-1.0 error give a tip about using
+    --with-async-mode with the libftdi package when erroring out.
+
 2010-06-21  Mike Frysinger  <vapier@gentoo.org>
 
   * src/bus/bf518f_ezbrd.c (urj_bus_bf51x_bus): Fix copy & paste typo in name.

urjtag/configure.ac

@@ -282,7 +282,8 @@ AS_IF([test "x$with_libftdi" != xno], [
     HAVELIBFTDI_ASYNCMODE=yes
   ], [
     AS_IF([test "x$HAVELIBUSB1" = "xyes"], [
-      AC_MSG_ERROR([this libftdi cannot be used with libusb-1.0, libusb-0.1 is needed])
+      AC_MSG_ERROR([this libftdi cannot be used with libusb-1.0, libusb-0.1 is needed.
+                    did you configure libftdi with --with-async-mode ?])
     ],)
   ])
 ],)