updated owner change function.
PreciousStone's changeOwner function does not carry out all the necessary process to complete the owner change.
MyPreciousStone's changeowner method now compensate this and complete owner change.
Note: the new command:
/myps changeowner <oldowner> <newowner> : changes the ownership of the field, you're currently standing in from <oldowner> to <newowner>
/myps changeowner_all <oldowner> <newowner> : changes the ownership of all fields from <oldowner> to <newowner>