[MERGE] Move RemoteRepository caching logic to CachedParentsProvider

[Aaron Bentley]

Andrew Bennetts wrote:
> Aaron Bentley wrote:
>> Andrew Bennetts wrote:
>>> But in practice I
>>> don't think anyone really cares about the difference between FAIL and ERROR;
>>> either way the test failed, and the distinction only matters as a hint for
>>> debugging why.
>> Some test runners draw distinctions that make the difference painful.
> 
> Really?  They sound buggy.  It's difficult to run bzr's tests with anything
> other than the builtin runner at the moment anyway.

nosetests for example has:

  --pdb                 Drop into debugger on errors
  --pdb-failures        Drop into debugger on failures

>> Do you want me to apply the patch I attached?
> 
> I'd prefer just a plain AssertionError to further bloating errors.py.  I
> believe Martin has previously stated that we should try to avoid adding
> errors that we never intend to catch.

Done.

Aaron