[nomaster] SI-7733 reflective packages now more consistent with scalac

Previously PackageScopes from scala.reflect ignored all classes that
had $'s in non-rightmost positions in their names.

Unfortunately this behaviour is inconsistent with how scalac does things,
and I reconciled this as usual, by pulling corresponding logic into
scala-reflect.jar and sharing it between runtime reflection and compiler.

This change has seprate pull requests for 2.10.x and 2.11.0. The latter
deprecates `scala.tools.nsc.util.ClassPath.isTraitImplementation`
whereas the former (which you're looking at right now) does not, because
we can't deprecated members in minor releases.
Merge pull request #2809 from xeno-by/ticket/7733

SI-7733 reflective packages now more consistent with scalac