Desugared context bounds visible in scaladoc

[Kordyjan]

See for example http://dotty.epfl.ch/api/scala/collection/ArrayOps.html#++:-fffff732
evidence$15 is generated name and shouldn't be present in a signature.

[cayhorstmann]

This should really be displayed as def ++:[B >: A : ClassTag](prefix: Array[_ <: B]) like in the source.