Fixed Yaml loader/dumper to use underscores
bug #10686 Fixing Yaml Loader/Dumper to use underscores instead of dashes (WouterJ)

This PR was merged into the 2.5-dev branch.

Discussion
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Fixing Yaml Loader/Dumper to use underscores instead of dashes

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Commits
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9ba2861 Fixed Yaml loader/dumper to use underscores