Bringing a bit of order to symbol substitution.

Painstakingly winnowed out the most frequently duplicated code sequences
related to symbol cloning and substitution. Created canonical methods to
perform these actions and documented them. Key methods include:

  def createFromClonedSymbols[T](syms: List[Symbol], tpe: Type)(creator: (List[Symbol], Type) => T): T
  def deriveSymbols(syms: List[Symbol], symFn: Symbol => Symbol): List[Symbol]
  def deriveType(syms: List[Symbol], symFn: Symbol => Symbol)(tpe: Type): Type

Many example usages enclosed with commit.

I did lots of timing tests, I find no material difference before and
after. Actually I won by four seconds in this incarnation:

  Before - Total time: 7 minutes 55 seconds
   After - Total time: 7 minutes 51 seconds

Review by moors.

1 files changed, 2 insertions, 7 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Implicits.scala b/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
index 2c32d22081..b67198a292 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
@@ -297,8 +297,7 @@ trait Implicits {
         case _ => tp
       }
       def stripped(tp: Type): Type = {
-        val tparams = freeTypeParametersNoSkolems.collect(tp)
-        tp.subst(tparams, tparams map (t => WildcardType))
+        deriveTypeWithWildcards(freeTypeParametersNoSkolems.collect(tp))(tp)
       }
       def sum(xs: List[Int]) = (0 /: xs)(_ + _)
       def complexity(tp: Type): Int = tp.normalize match {
@@ -371,11 +370,7 @@ trait Implicits {
 
     /** The type parameters to instantiate */
     val undetParams = if (isView) List() else context.outer.undetparams
-
-    def approximate(tp: Type) =
-      if (undetParams.isEmpty) tp
-      else tp.instantiateTypeParams(undetParams, undetParams map (_ => WildcardType))
-
+    def approximate(tp: Type) = deriveTypeWithWildcards(undetParams)(tp)
     val wildPt = approximate(pt)
 
     /** Try to construct a typed tree from given implicit info with given