Comparison with Boolean literals is currently not supported

[maxkratz]

Possibly related to #75

---

this

mapping n2n with mapVnode {
	var b : EBoolean
};

constraint -> mapping::n2n {
	self.variables().b == true
}

does produce an error:

Multiple markers at this line

• Boolean expression does not evaluate to boolean.
• no viable alternative at input 'true'