What does this implement/fix? Explain your changes.

Use UTF8 explicitly to marshal strings towards Python C-API functions ending in String.

Does this close any currently open issues?

#979.

Any other comments?

Runs fine for me both with 2.5.1 as well as current master on Linux.

Checklist

Check all those that are applicable and complete.

• Make sure to include one or more tests for your change
• If an enhancement PR, please create docs and at best an example
• Add yourself to AUTHORS
• Updated the CHANGELOG