Revert "BUG: Do not rely on an exception message. Look at the CTrait itself to determine if the exception came from an Event trait or not."

This reverts commit 6954ff0130e6d3fb800f4c20454f96328ecceb37.
ENH: Make a note of why parsing the exception message is necessary.
ENH: Test the fixed bug.
Merge branch 'master' into fix-event-delegate
Update change log.
Merge pull request #123 from enthought/fix-event-delegate

Fix event delegate