Support native Python 3.4 enums with enum type

[Veeti Paananen]

It would be nice to have built-in integration between the SQLAlchemy enum type and standard Python enums.

[Mike Bayer]

easy enough for whomever wants to PR it

[Mike Bayer]

some discussion at https://bitbucket.org/zzzeek/sqlalchemy/pull-request/51/builtin-enum-recipe/diff.

My current proposal is to add a minimal integration hook as:

from any_enum_package import Enum
class Color(Enum):
    red = 1
    green = 2
    blue = 3

enum_type = sqlalchemy.Enum('red', 'green', 'blue', enum_obj=(Color.red, Color.green, Color.blue))

The Enum type would now deal with "Color.red", "Color.green", and "Color.blue" as the values which are expected as input as well as delivered in output.

[Mike Bayer]

• add changelog and migration notes for new Enum features, fixes #3095, #3292
• reorganize enum constructor to again work with the MySQL ENUM type
• add a new create_constraint flag to Enum to complement that of Boolean
• reinstate the CHECK constraint tests for enum, these already fail /skip against the MySQL backend
• simplify lookup rules in Enum, have them apply to all varieties of Enum equally

→ <<cset df55695f8e99>>