add debugging output to server and waiting client

server shows level when the game starts, on debug channel
mp client which is waiting shows allow_changes value
server debugging output: show level cfg when adding player
add debugging output to mp clients when add new player
fix bug #21916, ready blocked at inappropriate times

the problem was that params.saved_game was checked at the wrong time,
it was checked at the time of making a new config, but not in the
constructor. the result is that the host and clients are out of sync
about whether allow_changes is true for a given side.