GROOVY-6945: Some DGM Collection improvements
Merge pull request #483 from paulk-asert/groovy6945

GROOVY-6945: Some DGM Collection improvements
GROOVY-6948: NioGroovyMethods don't work under JDK6
minor refactor (code cleanup)
GROOVY-6953: Fix regression in static compilation wrt to @DelegatesTo and maps