[mythtv-cmyth] Release v1.8.12

This updates the MythTV PVR addon to v1.8.12. 

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Changelog:

- Added 'Delete and re-record' menuhook
- Added support for MythTV protocol 76 and 77 (MythTV 0.27)
- Allow the backend to shutdown (by using monitor and playback connections)
- Reduced startup time (Faster loading of channels)
- Fixed start time for instant recordings
- Fixed several smaller memory and multithreading issues
- Refactored & cleaned up libcmyth (epginfo)