Accommodate Scala2 name resolution scheme

Scala2 does not conform to spec Section 2, where it says:

Bindings of different kinds have a precedence defined on them:

 1. Definitions and declarations that are local, inherited, or made available by a package clause and also defined in the same compilation unit as the reference, have highest precedence.
 2. Explicit imports have next highest precedence.
 3. Wildcard imports have next highest precedence.
 4. Definitions made available by a package clause, but not also defined in the same compilation unit as the reference, have lowest precedence.

In fact Scala 2, merges (1) and (4) into highest precedence.

This commit simulates the Scala2 behavior under -language:Scala2, but gives a migration
warning. For the naming-resolution test case we get:

    dotc *.scala -language:Scala2 -migration
    callsite.scala:9: migration warning: Name resolution will change.
     currently selected                     : naming.resolution.Files
     in the future, without -language:Scala2: java.nio.file.Files'

    where  Files   is a type in package object package which is an alias of java.util.stream.Stream[java.nio.file.Path]
           Files'  is a class in package file

      def gimmeFiles: Files = Files.list(Paths.get("."))
                      ^
    one warning found

0 files changed, 0 insertions, 0 deletions