Make MailerSpec use `eventually`
MemoizeSpec: apply(key, default) does not return a Box

No idea how this used to pass
Test for Props.testMode detection

Does not serve as a complete spec, only to assert that
during the current run the mode has indeed been
detected as "test."
Props: Add another specs2 class to test for
MailerSpec needs to touch Props.mode
Joni's fix for JsonBoxSerializer