Reference to field's type in initializer shouldn't result in invalid access errors

[bradcray]

Today, we don't permit references to fields within an init() rouitne before they're initialized, to avoid read-before-init errors. However, the current error-checking also prevents us from referring to the types of such fields (even when they have no runtime type information), which seems too strict. As an example (ATO):

record R {
  var x: int;

  proc init(y: x.type) {
    writeln(x.type:string);
    this.x = y;
  }
}

var myR = new R(y=42);
writeln(myR);

The two references to x.type before x is initialized generate warnings:

code.chpl:4: In initializer:
code.chpl:5: error: field "x" used before it is initialized
code.chpl:4: error: invalid access of class member in initializer argument list

but it seems like they shouldn't.