Made member function tables available as a globals

This way the scripts can add or replace existing member functions, which
can be useful. As demonstration chr_money and chr_money_change are now
added as Entity.money and Entity.change_money.

Also fixed the banker to use ask_number instead of ask_integer (I had
decided to rename this and apparently forgot the banker).

Mantis-issue: 503
Reviewed-by: Ablu