Groovysh: GROOVY-7200 + GROOVY-7201

These are tiny improvements / cleanups to Groovysh. 7200 changes one API (the constructor of GroovySyntaxCompletor), so you might not want to add this to groovy-2.3.x based on principles.

But I would suggest applying them all, not sure who else would ever want to construct an instance of that completor and could be have their code broken.