Wrong error: Tuple assignment only allowed when rhs is a function call

[Adrian Pop]

If we have an external function that returns a tuple:

equation 
  (del, -vx) = ExternalFunc1(val); 

we get this error:

Tuple assignment only allowed when rhs is a function call.

This worked in 1.5.0 (but no longer works in trunk).
The bug was reported here:

​http://www.openmodelica.org/index.php?option=com_agora&task=topic&id=132&Itemid=87

[Martin Sjölund]

It shouldn't work! An error message explaining why should be added.
(Tuple assignments only allow expression or tuple of crefs on lhs)

There also seems to be bugs when calling:
del = ExternalFunc1(val); (If val is constant... Works as expected, (del,_) = ExternalFunc1(val) if val is not constant)

[AlexeyLebedev]

Added a new error message for tuple assignments where lhs tuple contains not only component references in revision 6449.
del = ExternalFunc1(val) and (del,_) = ExternalFunc1(val) work fine for me even if val is not constant.