Better method name for `not a subclass` type constraint
Better method name for `not a subclass` type constraint

The !<:< type constraint works by causing an ambiguous implicit when
the constraint is not satisfied. Unfortunately, ambiguous implicits
do not activate the `implicitNotFound` annotation. When the compile
fails with an ambiguous implicit, it only prints the names of the
matching implicit methods. So, it makes sense for us to put a
helpful message in the method names themselves.

(sapling split of 897f80e5c385a61c9e7407df33906f1fb43516f7)
foursquare/fsqio,foursquare/fsqio,foursquare/fsqio,foursquare/fsqio,foursquare/fsqio