Store and display a definition file's mtime.

Note: It's now required to use ISO 8601 format for that string.

EX: date -u '+%Y-%m-%dT%H:%M:%S.0Z'
ds2-dump: Reuse the --ecu argument for --list-operations.
Migrate to using POSIX style stuff for serial port comms.

This frees us up to pass around raw file descriptors so that we can
use BT-RS232 adapters on Android.
Schema: Enforce uniqueness constraints on operations and results.
Add LGPL 3.0 blurbs to source files.