EMI: fix pause handling

On vista point it may happen that two sequences for the rock landings
are executed at the same time. Although they intend to be locked via
pause_scripts(), changing the set will call unpause_scripts() and unlock
all of them.

The patch will use the optional parameter for (un)pause_scripts() to
determine whether the calls should be "recursive" (e.g. when switching a
set or opening the inventory) or not