Remove known problem types from the variables panel.

Closures, PDO, Exceptions and XML have all caused us grief in the past.
Exclude these types from the panel data. Additionally, find and execute
any queries we can find so they don't cause issues either.

Refs #256
Fix up test bootstrap.
Fudge tests for TimedBehavior.

I think this is exposing an issue in Cake\ORM\Query and will have to
look further as I'm not sure.
Fix mistake in travis.yml.
Sort use statements.
Merge pull request #276 from cakephp/issue-256

Remove known problem types from the variables panel.