Assign memorial log in player assignment operator.

Reproduce:

Start with a new character, save game but don't exit the game.
Start a new character in the same world, save.
Look the the memorial dumps in save/<worldname>/#*.log

The second character has the memorial log of the first one, too.

Fixed by applying `player::memorial_log` in the assignment operator player.
During char gen `g->u` is assigned a new player object, but the memorial_log would not be assigned and remained unchanged.

Fixes #6206