merge: shortcircuit filemerge for identical files
- use filectx.cmp to compare files
- move merge messages into filemerge
- kill the redundant resolving message
- update tests
abort: repository a not found!
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abort: error: Connection refused
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abort: repository a not found!
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abort: destination '../a' already exists
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abort: repository a not found!
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abort: destination 'q' already exists