MiniAOD 7.0.X fixes from CSA14 feedback

This set of small commits fixes individual issues that had been pointed out during CSA14 (mostly from https://twiki.cern.ch/twiki/bin/viewauth/CMS/MiniAODCSA14FollowUp)

While there's no change in the dataformats, these fixes really enter the miniAOD production step (unlike e.g. #4862 which was only affecting analysis on top of miniAODs), so to benefit from the fix one has to reproduce the miniAODs.
For the last commit, related to MET corrections, if somebody wants to implement something better feel free to leave it out. In the next two weeks I'll be at a conference and then on holidays, so I will be able to follow up on this PR only intermittently.

@arizzi