solve_ndisj: solve more goals involving chains of differences

This improves solve_ndisj to handle goals that came up in iris/examples as part of the logically atomic triple mask change.

mentioned in merge request !301 (merged)

added 3 commits

• 49d6a4f9...fa9692b2 - 2 commits from branch master
• d0176db3 - solve_ndisj: solve more goals involving chains of differences

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• b5adcbea - changelog

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resolved all threads

LGTM.

resolved all threads

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• 22a2d166 - more detailed changelog

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enabled an automatic merge when the pipeline for 22a2d166 succeeds

@iris-users this again makes solve_ndisj more powerful, so some proofs could break because more goals are closed by this tactic.

mentioned in commit e0de35f0

merged