fix for GRAILS-6813 "character encoding problem with message.properties in plugins"
Merge branch '2.1.x' into 2.2.x

Conflicts:
	grails-core/src/main/groovy/org/codehaus/groovy/grails/context/support/PluginAwareResourceBundleMessageSource.java
	grails-plugin-i18n/src/main/groovy/org/codehaus/groovy/grails/plugins/i18n/I18nGrailsPlugin.groovy