Overrides Java launch method to find existing Scala launches

Since Eclipes 3.8, a package private method is used by JavaLaunchShortcut
to find existing launch configurations for a given type.
Overrides the Java launch method to use different logic to find the Scala
launch configuraitons.

Fixes #1001447
Merge pull request #507 from skyluc/issue/new-config-each-run-1001447

Overrides Java launch method to find existing Scala launches