mode_RPiHQ_mean.cpp: misc changes
mode_RPiHQ_mean.cpp: misc changes

Added error check for history arrays too small.
Changed Log() levels to match ZWO exposure Log() entries (from 2 to 3).
Clarified a few Log() messages.
thomasjacquin/allsky,thomasjacquin/allsky,thomasjacquin/allsky