Refactoring of envelope from setting, to fit with other code updates and to enable setting via sendMail closure:
sendMail {
    envelopeFrom '...'
}

See http://www.pither.com/articles/2010/06/22/envelope-senders-for-grails-mail-plugin-spring-java-mail
Add simple unit test for envelopeFrom
Object to using envelopeFrom without JavaMailSender
Integration tests to cover envelopeFrom use
Tabs not spaces for consistency.
Stronger typing of GreenMail
Merge branch 'master' of github.com:spither/grails-mail into spither-master

Conflicts:
	test/integration/grails/plugin/mail/MailServiceTests.groovy
Merge branch 'spither-master'
Merge branch 'master' of github.com:gpc/grails-mail