tests: make pdiff return appropriate exit code at comparison of files
Before this patch, pdiff script returns 0, even if diff is detected.
This issue doesn't cause failure of tests using it, if it is invoked
via extdiff extension, because extdiff itself examines changes between
specified revisions and decides exit code.
BTW, this patch ignores recursive comparison case, because:
- there is no portable way for current while-read based
implementation to return 1 at detecting changes
- it isn't yet needed to replace direct "diff -r" invocation by
pdiff for portability
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https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
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If you can't run the entire testsuite for some reason (it can be
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any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).