Checking if a page is available before trying to add error message to it. This replaces a try-catch because in occasions a FinalException was being thrown, with apparently cannot be caught.
Merge dev into feature/809-finalexception-not-caught
Merge pull request #1007 from SalesforceFoundation/feature/809-finalexception-not-caught

Feature/809 finalexception not caught
Merge dev into feature/362-trial-walkthrough