Bump to Scala 2.11.0-M7

  - reported and worked around SI-8023
  - exclude incorrect transitive dependencies of scala-compiler
  - Use sbinary published against 2.11.0-M4, for now

All modules compile.
Revert workaround for the now-fixed inference bug, SI-7688

Partially reverts e6437fdcc707
Revert workarounds (?) that aren't needed in 2.11.0-M7

Partially reverts e6437fdcc707