Duplicate parameter name causes exception

[lupuchard]

func foo(a int, a int) int { }

throws assertion failed exception with little info:

Exception in thread "main" Assertion failed! Assertion failed!
	at dev.vale.vfail$.apply(vassert.scala:100)
	at dev.vale.vassert$.apply(vassert.scala:44)
	at dev.vale.vassert$.apply(vassert.scala:39)
	at dev.vale.postparsing.VariableDeclarations.<init>(VariableUses.scala:23)
	at dev.vale.postparsing.VariableDeclarations.$plus$plus(VariableUses.scala:26)
	at dev.vale.postparsing.FunctionScout.$anonfun$scoutTopLevelFunction$13(FunctionScout.scala:122)
	at scala.collection.TraversableOnce.$anonfun$foldLeft$1(TraversableOnce.scala:157)
	at scala.collection.TraversableOnce.$anonfun$foldLeft$1$adapted(TraversableOnce.scala:157)
	at scala.collection.Iterator.foreach(Iterator.scala:944)
	at scala.collection.Iterator.foreach$(Iterator.scala:944)
	at scala.collection.AbstractIterator.foreach(Iterator.scala:1432)
	at scala.collection.IterableLike.foreach(IterableLike.scala:71)
	at scala.collection.IterableLike.foreach$(IterableLike.scala:70)
	at scala.collection.AbstractIterable.foreach(Iterable.scala:54)
	at scala.collection.TraversableOnce.foldLeft(TraversableOnce.scala:157)
	at scala.collection.TraversableOnce.foldLeft$(TraversableOnce.scala:155)
	at scala.collection.AbstractTraversable.foldLeft(Traversable.scala:104)
	at dev.vale.postparsing.FunctionScout.scoutTopLevelFunction(FunctionScout.scala:122)
	...