checkplot: output pickle now version 3 instead of HIGHEST_PROTOCOL
checkplot: output pickle now version 3 instead of HIGHEST_PROTOCOL

this made the pickles created in Python 3.5+ unreadable in Python 2.7.
should check for this problem elsewhere.


Former-commit-id: 910f28a6900498dd0958f5b6d7d9e56ed4c3ae5f
lgbouma/astrobase,lgbouma/astrobase,lgbouma/astrobase,waqasbhatti/astrobase,waqasbhatti/astrobase,waqasbhatti/astrobase