Merge pull request #210 from ranterle/master

Document the new Servlet API requirements in Grails 2.4
Update whatsNew24.gdoc

fix some typos, etc.
Update whatsNew24.gdoc

catch up with a recent commit
Merge pull request #211 from kgeis/patch-1

Update whatsNew24.gdoc
GRAILS-11453 - document traits for exception handlers
GRAILS-11428 update HibernateTestMixin example
GRAILS-11452 GRAILS-11428 basic docs for HibernateTestMixin, update domain class unit testing docs
workaround for doc rendering bug
GRAILS-11491 GRAILS-11354 GRAILS-11462 - document getObjectToBind
trivial cleanup
Pivotal img assets