This introduces Python 3 compatibility for Django Evolution. Most of the

work needed for compatibility has been introduced in prior commits, and

this change handles the remaining syntactical and string differences.
One of the highlights is that the default Pickle protocol changed

(twice) in Python 3. We now force usage of protocol 0, which is an

ASCII-based payload format and the default in Python 2.
There's also a difference in default string types used for Django field

names. Unless otherwise explicitly set, field names (used for indexes

and other parts of the schema definitions) are based on the attribute

name in the model, which on Python 2 is a byte string and on Python 3 is

a unicode string. To get the right string type on each Python version,

we convert the names to the native string type using str(). We don't

want or need to actually encode or decode -- str() is the most

compatible way here.
The rest of the changes mostly have to do with exception handling, print

statements, and removing/adding prefixes on certain string types.
There's still work that's needed on getting all the management commands

fully tested. That will be part of upcoming changes.

Unit tests pass on Django 1.6 through 1.11, with all database types.
Tested Python 3.4, 3.5, and 3.6 with Django 1.6, 1.7, and 1.11 (aiming

to test a spectrum of the changes).