remove limitation: two or more overloaded variants of method have default arguments

[hsn10]

remove limitation: two or more overloaded variants of method have default arguments

so we can have code like this

class T1() {
  def f(a: Int, b: Char) = {}
  def f(a: Int, b: String, c: String = "pepa") = {}
  def f(a: String, b: String, c:String = "karel") = {}
}