Patch for unittest on trunk.
It provides better default failure messages for assertTrue and
assertFalse (current is "AssertionError: None").
It also provides a new class attribute for TestCase: longMessage
This defaults to False. If set to True, passing in an explicit custom
message does *not* override the helpful default failure message in
asserts which tell you which objects were involved in the failure.
Even if set to True or False in a TestCase then longMessage can still be
overridden in individual tests by setting an instance attribute.
Needs docs.
Could longMessage default to True in 3.1.

Reviewers: ,
Description:
Patch for unittest on trunk.
It provides better default failure messages for assertTrue and
assertFalse (current is "AssertionError: None").
It also provides a new class attribute for TestCase: longMessage
This defaults to False. If set to True, passing in an explicit custom
message does *not* override the helpful default failure message in
asserts which tell you which objects were involved in the failure.
Even if set to True or False in a TestCase then longMessage can still be
overridden in individual tests by setting an instance attribute.
Needs docs.
Could longMessage default to True in 3.1?
Please review this at http://codereview.appspot.com/32102
Affected files:
   Lib/test/test_unittest.py
   Lib/unittest.py
   Misc/NEWS

Updated patch with better docstring for _formatMessage and docs.
Patch reviewed by Brett Cannon so will commit.

messages: + msg85150