nb: still does not work for nested iterators

I think it is  safe to suppose that the node is on  the base clock in
this case.

The dependency on the clock was lost when the enum is translated into
an integer (because some expression were still refering to the enum type).

The fix was to index VarMap.t by string instead of Soc.var_expr in ActionsDeps.

such as in the equation
 o1,o2 = current (n(x,y,z));