Sharpen a type in Inliner

[odersky]

Replace some MemerDefs by ValorDefDefs.

[odersky]

@nicolasstucki I remembered the reason why we should not inline by-name-parameters before typing: The by-name parameter might appear multiple times in different branches of an inline match or inline if. For instance, here's the case of the trace.conditionally macro:

  def conditionally[TC](cond: Boolean, question: => String, show: Boolean)(op: => TC)(implicit ctx: Context): TC =
    if (Config.tracingEnabled) {
      def op1 = op
      if (cond) apply[TC](question, Printers.default, show)(op1)
      else op1
    } else op

op (which is usually a large expression) appears twice in the body. After typechecking the inner if, only one branch will remain, since Config.,tracingEnabled is an inline val. But if we substitute immediately, we create and typecheck two copies of the argument.