machinetalk/mkwrapper: fix of possible value underrun due to possible unsubscribe
machinetalk/mkwrapper: fix broken error handling in preview class
Merge pull request #350 from strahlex/mkwrapper-fix2

Mkwrapper fixes
machinetalk/mkwrapper: replacing unnecessary subscription counters
Merge pull request #351 from strahlex/mkwrapper-fix2

Addition to previous mkwrapper fix
Merge branch 'master' of https://github.com/machinekit/machinekit.git