Enabled more tests on Travis

Ref #235

I've enabled DB (MySQL, PostgreSQL, SQLite) tests and Memcache(d).

The good thing is, that more tests are run:
```
Zend/Auth/AllTests.php
79 -> 100

Zend/Cache/AllTests.php
215 -> 295

Zend/Db/AllTests.php
243 -> 2332
```

There is a bad thing though - some of the newly run tests are failing.