More logging for divergent implicits
SI-8460 A failing test case extracted from shapeless

This used to work in 2.10.x. I believe that 2.11.x is correct to
stop the implicit search on account of divergence.

	[log typer] deferring divergence error: diverging implicit expansion for type DeepSearchExamples.Searchable[((String,),),String]

	Implicit search stack:
	seeking type `DeepSearchExamples.Searchable[((String,),),String]` with method hlistishSearchable in object DeepSearchExamples
	  seeking type `DeepSearchExamples.Searchable[shapeless.::[(String,),shapeless.HNil],String]` with method hlistishSearchable in object DeepSearchExamples
	    seeking type `DeepSearchExamples.Searchable[shapeless.::[(String,),shapeless.HNil],String]` with method hlistishSearchable in object DeepSearchExamples
	[log typer] A subsequent divergent error occured, we can no longer ignore: diverging implicit expansion for type DeepSearchExamples.Searchable[((String,),),String]

	Implicit search stack:
	seeking type `DeepSearchExamples.Searchable[((String,),),String]` with method hlistishSearchable in object DeepSearchExamples
	  seeking type `DeepSearchExamples.Searchable[shapeless.::[(String,),shapeless.HNil],String]` with method hlistishSearchable in object DeepSearchExamples
	    seeking type `DeepSearchExamples.Searchable[shapeless.::[(String,),shapeless.HNil],String]` with method hlistSearchable in object DeepSearchExamples
	[log typer] implicit adapt failed: diverging implicit expansion for type DeepSearchExamples.Searchable[((String,),),String]

I have also included a re-worked version that does compile.
That version guides implicit search by using implicit prioritization
to help implicit search prune the search before hitting the
divergent case.