message: Update configure to reject unsafe miniUPnPc API ver
  Also fixes behavior when libminiupnpc is not installed.
diff: @@ -928,6 +928,26 @@ if test x$use_upnp != xno; then
  [AC_CHECK_LIB([miniupnpc], [upnpDiscover], [MINIUPNPC_LIBS=-lminiupnpc], [have_miniupnpc=no])],
  [have_miniupnpc=no]
  )
  +dnl The minimum supported miniUPnPc API version is set to 10. This keeps compatibility
  +dnl with Ubuntu 16.04 LTS and Debian 8 libminiupnpc-dev packages.
  +if test x$have_miniupnpc != xno; then
  + AC_MSG_CHECKING([whether miniUPnPc API version is supported])
  + AC_PREPROC_IFELSE([AC_LANG_PROGRAM([[
  + @%:@include <miniupnpc/miniupnpc.h>
  + ]], [[
  + #if MINIUPNPC_API_VERSION >= 10
  + // Everything is okay
  + #else
  + # error miniUPnPc API version is too old
  + #endif
  + ]])],[
  + AC_MSG_RESULT(yes)
  + ],[
  + AC_MSG_RESULT(no)
  + AC_MSG_WARN([miniUPnPc API version < 10 is unsupported, disabling UPnP support.])
  + have_miniupnpc=no
  + ])
  +fi
  fi
  BITCOIN_QT_INIT
  @@ -1326,9 +1346,10 @@ dnl enable upnp support
  AC_MSG_CHECKING([whether to build with support for UPnP])
  if test x$have_miniupnpc = xno; then
  if test x$use_upnp = xyes; then
  - AC_MSG_ERROR("UPnP requested but cannot be built. use --without-miniupnpc")
  + AC_MSG_ERROR("UPnP requested but cannot be built. Use --without-miniupnpc.")
  fi
  AC_MSG_RESULT(no)
  + use_upnp=no
  else
  if test x$use_upnp != xno; then
  AC_MSG_RESULT(yes)
  