Add some tests for email modules

[Sorin Marian Nasoi]

If for instance we add tests that check if a correct error is raised (for instance that there is no SMTP server in case of the SMTP module or there is no email server in case of the IMAP module) then at least part of the functionality would be tested.

As a result:
- we check that the module is loaded, the functions exists, and at least the code that should raise some errors also works

Off course these kind of tests do not assure that the functions work 100%, but IMHO some checking is better than none: what do you think?