Prevent Race Condition in mkImplicitConversionAnnotation

Fix #1002269.
Merge pull request #803 from huitseeker/issue/1002269

Prevent Race Condition in mkImplicitConversionAnnotation
Cleanup locate() and friends.

Signed-off-by: François Garillot <francois.garillot@typesafe.com>
Presentation compiler elements for ScalaDoc
Adding Presentation compiler tests, including inherited & param symbols
Completion Integration for ScalaDoc
Integration of scalaDoc with ScalaHover.

ScalaDoc is only obtained through F2.
make Hover debug layer point to getHoverInfo2.

Reestablished Scaladoc on Hover
Thanks @sschaef for the fix !

Fix #1000453, Fix #1000210.