[BUG #7325] leave debug output in for the mmt
[BUG #7325] make client send its last-check-time

- correct reload behavior if clients keep their last check time
- supports multiple concurrent clients
- use inital load time as last check time (if something changed it's reloaded
  anyway), this chatches small-margin misses
- expose web-server/server-port in SOURCE_SERVER_PORT macro