Poking around at SI-5265.

Advances the test from a crasher to an inference failure.

Here's how it rolls.

```
  ~/code/scala ./build/quick/bin/scalac -Yinfer-debug test/files/pos/t5845.scala[solve types] solving for T, CC in ?T, ?CC
[infer method] solving for T, CC in (lhs: T)(implicit num: CC[T])num.Ops based on (Int)(implicit num: CC[T])num.Ops (solved: T=Int)
inferExprInstance {
  tree      A.this.infixOps[Int, CC](5)
  tree.tpe  (implicit num: CC[Int])num.Ops
  tparams   type CC
  pt        ?
}
[solve types] solving for CC in ?CC
inferExprInstance/AdjustedTypeArgs {
  okParams   type CC
  okArgs     [X]Num[X]
  leftUndet
}
[infer implicit] A.this.infixOps[Int, [X]Num[X]](5) with pt=Num[Int] in class A
[search] A.this.infixOps[Int, [X]Num[X]](5) with pt=Num[Int] in class A, eligible:
  n1: => Num[Int]
[search] considering no tparams (pt contains no tvars) trying Num[Int] against pt=Num[Int]
[success] found SearchResult(A.this.n1, ) for pt Num[Int]
[infer implicit] inferred SearchResult(A.this.n1, )
[infer implicit] <empty> with pt=scala.languageFeature.higherKinds in class A
companionImplicitMap scala.languageFeature.higherKinds{ }
[infer implicit] inferred SearchResult(<empty>, )
[infer implicit] <empty> with pt=scala.languageFeature.implicitConversions in class A
companionImplicitMap scala.languageFeature.implicitConversions{ }
[infer implicit] inferred SearchResult(<empty>, )
warning: there were 2 feature warnings; re-run with -feature for details
one warning found
```

```
  ~/code/scala ./build/quick/bin/scalac -Yinfer-debug test/files/pos/t5845.scala
[infer view] 5 with pt=Int(5) => ?{def +++: ?} in class A
[search view] 5 with pt=Int(5) => ?{def +++: ?} in class A, eligible:
  infixOps: [T, CC[X] <: Num[X]](lhs: T)(implicit num: CC[T])num.Ops
[solve types] solving for T, CC in ?T, ?CC
[infer method] solving for T, CC in (lhs: T)(implicit num: CC[T])num.Ops based on (Int)(implicit num: CC[T])num.Ops (solved: T=Int)
[search] considering no tparams (pt contains no tvars) trying (lhs: Int)(implicit num: CC[Int])num.Ops against pt=Int(5) => ?{def +++: ?}
[success] found SearchResult(A.this.infixOps[Int, CC], ) for pt Int(5) => ?{def +++: ?}
[infer implicit] inferred SearchResult(A.this.infixOps[Int, CC], )
[infer implicit] A.this.infixOps[Int, CC](5) with pt=CC[Int] in class A
companionImplicitMap CC[Int] {
  class Int  int2double: (x: Int)Double, int2float: (x: Int)Float, int2long: (x: Int)Long
}
[infer implicit] inferred SearchResult(<empty>, )
[infer view] () with pt=Unit => CC[Int] in class A
companionImplicitMap Unit => CC[Int] {
  class Int  int2double: (x: Int)Double, int2float: (x: Int)Float, int2long: (x: Int)Long
}
[infer implicit] inferred SearchResult(<empty>, )
[infer view] () with pt==> Unit => CC[Int] in class A
companionImplicitMap => Unit => CC[Int] {
  class Int  int2double: (x: Int)Double, int2float: (x: Int)Float, int2long: (x: Int)Long
}
[infer implicit] inferred SearchResult(<empty>, )
[infer view] 5 with pt=Int(5) => ?{def +++(x$1: ? >: Int(5)): ?} in class A
companionImplicitMap Int(5) => ?{def +++(x$1: ? >: Int(5)): ?} {
  class Int  int2double: (x: Int)Double, int2float: (x: Int)Float, int2long: (x: Int)Long
}
[infer implicit] inferred SearchResult(<empty>, )
[infer view] 5 with pt==> Int(5) => ?{def +++(x$1: ? >: Int(5)): ?} in class A
companionImplicitMap => Int(5) => ?{def +++(x$1: ? >: Int(5)): ?} {
  class Int  int2double: (x: Int)Double, int2float: (x: Int)Float, int2long: (x: Int)Long
}
[infer implicit] inferred SearchResult(<empty>, )
test/files/pos/t5845.scala:9: error: value +++ is not a member of Int
  5 +++ 5
    ^
[infer implicit] <empty> with pt=scala.languageFeature.higherKinds in class A
companionImplicitMap scala.languageFeature.higherKinds{ }
[infer implicit] inferred SearchResult(<empty>, )
[infer implicit] <empty> with pt=scala.languageFeature.implicitConversions in class A
companionImplicitMap scala.languageFeature.implicitConversions{ }
[infer implicit] inferred SearchResult(<empty>, )
one error found
```