[MERGE] Move RemoteRepository caching logic to CachedParentsProvider

[Aaron Bentley]

Andrew Bennetts wrote:
> Aaron Bentley wrote:
> We can (and arguably should) change the failureException on
> bzrlib.tests.TestCase to be a subclass of AssertionError.  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.

Do you want me to apply the patch I attached?

Aaron