Simplify deprecation machinery: don't cache previous messages, and use warnings instead of logging.
Add an assertIssuesDeprecationWarning method to UnittestTools, and test it.
Comment and style fixes; fix copyright header in deprecated.py.
Rename: assertIssuesDeprecationWarning -> assertDeprecated.
Test that 'assertDeprecated' fails when appropriate.
Add reference to related Python issue.
Add tests for 'deprecated' decorator with functions and methods.
Flake8, style.
Import unittest from unittest_tools so that we have the full range of assert methods available on Python 2.6.
Add CHANGES.txt entry.
Merge pull request #220 from enthought/feature/simpler-deprecations

Simplify deprecation machinery: don't cache previous messages, and use warnings rather than logging.