migrates to 2.11.0-RC1

This pull request migrates the scala-2.11.x branch to be compatible with the recently merged scala/scala#3452.

Currently `sbt clean compile test` using `2.11.0-SNAPSHOT` isn't going to work because of SI-8316. https://github.com/scala/scala/pull/3569 fixes that, and I've successfully checked that a minute ago.