Compiler.parseTree still not thread-safe

[scabug]

This is a similar problem as resoved in #8030. It is reported in the issue tracker of the Scala IDE.

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-8163?orig=1
Reporter: @sschaef
Affected Versions: 2.11.0
See #8030