fix functional test
GRAILS-10280: compilation under windows fixed
GRAILS-9162 - Improve @Validateable testing

Only modify ValidationErrors.metaClass.getAt if mockForConstraintsTests is called
Merge branch 'master' of github.com:grails/grails-core
remove @CompileStatic to allow code to compile
Merge pull request #375 from dmurat/GRAILS-10280

GRAILS-10280: compilation under windows fixed