This will only return the module name if it is inside a spades call,
i.e., it will return NULL if used in interactive mode.
The related function currentModule is simply a rapid accessor for the
current module name. This latter will return the module that is in the current
event queue, which will never be NULL.
.callingModuleName(sim)
# S4 method for class 'simList'
.callingModuleName(sim)
currentModule(sim)
# S4 method for class 'simList'
currentModule(sim)
.callingFrameTimeunit(x).callingModuleName returns the name of the module that is currently
the active module calling functions like scheduleEvent.