detect when USB serial adapters have been pulled on OSX
(was spinning in poll())
Add basic link state routing
Add AUTHTOKEN monitor notification
Replace AUTHTOKEN interface with AUTHSTART/AUTHNEXT

AUTHSTART initialises the authentication system. AUTHNEXT generates a
random 64bit number using XSalsa20 as a CSPRNG, and sends it on the
monitor interface via AUTHRAND. Moving the random number generation to
servald ensures compatibility across all frontends, and allows us to
easily access the (fast!) NaCl XSalsa20 implementation.