FragmentChecker should reject secondary constructor

[mario-bucev]

The following snippet is accepted, but it should be rejected because we do not handle secondary constructors at the moment:

object FragmentChecker {
  case class Test(val smth: Int, val other: Int) {
    def this(smth: Int) = this(smth, 42)
  }

  def test(x: Int) = {
    val t = new Test(x)
  }
}

We get a strange well-formedness error:

[ Error  ] FragmentChecker.scala:9:5: Type error: val t$63: Test$0 = Test$0(x$99)
[ Error  ] (), expected Unit,
[ Error  ] found <untyped>
[ Error  ] 
[ Error  ] Typing explanation:
[ Error  ] val t$63: Test$0 = Test$0(x$99)
[ Error  ] () is of type <untyped>
[ Error  ]   Test$0(x$99) is of type <untyped>
[ Error  ]     x$99 is of type Int
[ Error  ]   () is of type Unit
               val t = new Test(x)
               ^^^^^^^^^^^^^^^^^^^^