Disable context escape detection

I get very frequent build failures due to the mutual Scala<->Java dependency.
It builds for a long time, then decides that getCtx overrides nothing. The only
way to fix is another clean build. Total time lost: >5 minutes. These happened
occasionally before but have become much more frequent under ScalaIDe4.0, to the
point where this becomes a major drag on productity. Context escape detection
is nice but if it stops us getting work done, not worth the effort.
Merge pull request #312 from dotty-staging/disable-context-escape

Disable context escape detection