Allow future defs when printing with i"...".

We saw a failure of accessing a denotation outside its defined interval, which got triggered
by i"...". This should never be the case. We should be more interested in what i"..." has to print.

(V2, to see whether this builds with Travis now)

Author: odersky

src/dotty/tools/dotc/core/Decorators.scala

@@ -7,6 +7,7 @@ import Contexts._, Names._, Phases._, printing.Texts._, printing.Printer, printi
 import util.Positions.Position, util.SourcePosition
 import collection.mutable.ListBuffer
 import dotty.tools.dotc.transform.TreeTransforms._
+import typer.Mode
 import scala.language.implicitConversions
 
 /** This object provides useful implicit decorators for types defined elsewhere */
@@ -172,7 +173,7 @@ object Decorators {
       def treatSingleArg(arg: Any) : Any =
         try
           arg match {
-            case arg: Showable => arg.show
+            case arg: Showable => arg.show(ctx.fresh.addMode(Mode.FutureDefsOK))
             case _ => arg
           }
         catch {

src/dotty/tools/dotc/typer/InstChecks.scala

@@ -9,9 +9,10 @@ import Types._, Symbols._, Flags._, StdNames._
 import util.Positions._
 import ast.Trees._
 import typer.ErrorReporting._
+import DenotTransformers._
 
 /** This checks `New` nodes, verifying that they can be instantiated. */
-class InstChecks extends Phase {
+class InstChecks extends Phase with IdentityDenotTransformer {
   import ast.tpd._
 
   override def phaseName: String = "instchecks"