Fix aggregate handling for cascade deleted objects
Fix typo
Fix ambiguous column sorting
Add smart version checking, bump version
Fix error message
Fix random test fail
Add py34 to testing matrix
added default conversion
Merge pull request #88 from xymz/master

Fixed `PhoneNumberType` conversion bug
types: addition of EncryptedType

* Adds a type that has the name `EncryptedType`. This type gives
  the possibility to encrypt a value, so that in the database exists
  the encrypted form of the value and not the original one. When
  a value needs to be read(and is of type `EncryptedType`) the value
  automatically decrypted in order to present to the user.

* The encryption and decryption are using the AES algorithm which is
  implemented in pycrypto library. The minimum version of pycrypto
  is 2.0.1.

* Inside the tests folder there is a test whose name is
  `test_encrypted` and tests the functionality of the above type.

* Documentation is also written. Inside the `encrypted.py` file
  there is documentation with a complete example. Also the
  `data_types.rst` is modified in order to add a section for the
  `EncryptedType`.

Signed-off-by: Konstantinos Kostis <konstantinos.kostis@cern.ch>