Most of Django Evolution used standard Python 2 byte strings, which

prevented compatibility with Python 3 due to a series of assumptions

about string formats. These came into play primarily when hashing values

for index names (which resulted in different hashes for Unicode vs. byte

strings).
This change adds the unicode_literals import at the top of every file,

and updates tests/utils.py to force usage of byte strings for values

coming from the database test modules that would normally be byte

strings if coming from Django models, and to update mock_models.py to

convert field names to byte strings (for the same reason).

Unit tests pass on Django 1.6 through 1.11 with SQLite, Postgres,

and MySQL.