[MERGE] Prevent knit corruption by checking parents

[Andrew Bennetts]

On Thu, Sep 21, 2006 at 12:30:50PM -0400, Aaron Bentley wrote:
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> Aaron Bentley wrote:
> > This patch causes a KnitTextsDiffer exception to be raised when knits
> > disagree about the content of a parent.
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> Updated so that KnitTextsDiffer is a printable exception...

Perhaps add a test for it to test_errors?  Adding a short test for each new
error there is probably a good thing to do.

-Andrew.