v1.6.11

Verify against xrefactory sources and bump version to 1.6.11

Since c-xrefactory was a spin-off from xrefactory (non-open source)
1.6.9 and xrefactory, which somewhat still exists, are now at 1.6.10,
we needed to sync any bug fixes. There where none.

Now c-xrefactory is complete and can start its own journey.