Added autoconf/automake support for FTDI detection
autoconf/automake: add checks for gmtime_r and localtime_r

Redefined in owftpd unless defined properly here.
Added LINK v1.5 version
Added new LinkUSB master type, which uses libftdi to communicate directly to the device

The major upside is that we can set the "latency timer" of the FTDI chip, which improves communication speed greatly.
Next step is to run at 19200bps instead of 9600 (tested but not commitable code yet), which gives us speed comparable to the DS2480B.

Quick comparission: reading "power" on a DS18B20 takes 30ms with DS2480B, and 140ms with stock LinkUSB impl. With the impl + experimental 19200 code, we are down to 40ms.

TODO: cleanups and fixes, this is not "ready".