#11 guard conditions for transitions

[Rags Srinivasan]

Need to add support for adding guard conditions to
transtions. This gives the SM implementor app to
override framework's decition to whether or not take
the transition.

usage:
// in usage code
transition = smDef.createTransition(...);

// it is advisable the method has no side effect
Method m = MyApp.getMethod(...);
// add instead of set for supporting chaining
transition.addGuard(m);

// in framework code
// Event e
Transition t = find(...);

if(!t.evalGuard(e))
{
return ...;
}
do tranition;