Prevent launching when there are (Scala) build errors.

The base Java launcher wouldn’t prevent a lunch unless the error markers
were exactly jdt.core error markers. Scala error markers are subtypes of
the Java ones, so we re-implement the logic to stop the launch in this
case as well.

Fixed #3
Bump Tycho and Eclipse versions.
Merge pull request #4 from dragos/issue/launch-errors-3

Prevent launch when there are build errors