GC supports two download port types: serial ports and D2XX. Before, if
either of these failed to load, the download dialog wouldn't show either
port type. With this patch, if both fail, GC displays a warning, but if
either one succeeds, GC will proceed with only that port type. This
change should fix the problem that users were having to download and
install both the FTDI drivers and the PL2303 ones in order to download
from the SRM PCV.
I hate to change so many lines of code just for a little rename, but I want to
distinguish between "devices", like the PowerTap and SRM, and "communications
ports", like the serial port and the native D2XX drivers. This work is in
preparation for adding direct download support for the SRM.
