Deal with stdin in bordermultiplex.c

[OlegHahm]

So far stdin is not defined for all platforms (particular msp-430 is lacking a definition). Since it is used in bordermultiplex.c it should be either defined for all platforms (preferable) or replaced in this specific file.

[miri64]

The most elegant solution would be to define a UART transceiver/interface (see PR #460) and let the border router use another transceiver/interface instead of stdin, I think.

[LudwigKnuepfer]

Moved to
https://github.com/RIOT-OS/RIOT/blob/master/sys/net/network_layer/sixlowpan/border/bordermultiplex.c

[OlegHahm]

I guess we can close this one. There's a much better solution in the works by the NSTF.