Implicit search error should ideally explain type reduction process about splain

[tribbloid]

Now I have a prototype for this, the result looks promising:

(before)

newSource1.scala:8: error: implicit error;
!I e: Option[Int] =:= Option[String]
  Cannot prove that FoundReqVsImplicit.vecInt.Head =:= Option[String].

implicitly[vecInt.Head =:= Option[String]]
          ^
newSource1.scala:10: error: type mismatch;
  Option[String|Int]
val x: vecInt.Head = ??? : Option[String]
                         ^

(after)

newSource1.scala:8: error: implicit error;
!I e:
  Option[Int]
  .. (reduced from)
     FoundReqVsImplicit.vecInt.Head[Int]
  =:=
  Option[String]
  Cannot prove that FoundReqVsImplicit.vecInt.Head =:= Option[String].

implicitly[vecInt.Head =:= Option[String]]
          ^
newSource1.scala:10: error: type mismatch;
  Option[String|Int]
  .. (right side reduced from)
     FoundReqVsImplicit.vecInt.Head[Int]
val x: vecInt.Head = ??? : Option[String]
                         ^