Don't test tools on JDK6, Scala 2.11.x (closes #1235)

They lead to spurious failures. See ticket for details.
Upgrade default Scala version to 2.11.2
Upgrade partest to 1.0.1
Partially Upgrade to Scala 2.11.4 (closes #1204)
Merge pull request #1215 from gzm0/scala-2.11.4

Upgrade to Scala 2.11.4
Refactor JSEnv to support async running
Remove JSEnv constructor-blow up. Use default args
Add interface definition and tests for ComJSEnv.
Make RhinoJSEnv a ComJSEnv
Make NodeJSEnv a ComJSEnv
Clean up standalone sbt test project
Make preLinkJSEnv and postLinkJSEnv a task.

They might depend on a task such as update. On the other hand, they
are only used to run things, which arguably must be a task. Therefore,
it is safe to make them tasks.
Make PhantomJSEnv a ComJSEnv
rename to test interface
sbt compatible test iface definition