This efunction allows the interactive link to a given object to be
migrated to another object. That is, after a successful exec(to, from)
call, interactive(to) will return 1 and interactive(from) will return
0. The player that was controlling 'from' will begin controlling 'to'
following the exec() call. Note that this is a powerful function and
its use must be restricted if you wish to attempt to have a secure mud.
The proper way to restrict the use of exec() is to make a simul_efun of
the same name and then use valid_override(4) to restrict the use of a
simul_efun override (i.e. efun::exec()). The exec() function returns 1
if the switch is successful (and 0 otherwise).