ContainsAttributeValue missing __repr__ (issues useless errors)

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Use mox.ContainsAttributeValue comparator for a check that would fail
2. Run the test and get error printed

What is the expected output? What do you see instead?
Just like with the other Comparator classes, it should say something that tells 
what's wrong. Should contain at least what is checking. Instead it displays a 
useless generic Python description of the class instance:
+ function.__call__(<IgnoreArg>, <IgnoreArg>, <mox.ContainsAttributeValue 
instance at 0x8bb4b6c>) -> 0

From that message I cannot tell what attribute/value was expected and is 
missing.

What version of the product are you using? On what operating system?
Latest SVN has the same problem. Linux.

Original issue reported on code.google.com by di...@google.com on 1 Aug 2011 at 9:30