Patches ontop of PR1242, consistency fixes and conversions

The last two commits correspond to two patches to PF-egamma related work.

94693b9 addresses consistency issues when flipping to the PF-mustache super clusters (photons and reco::Conversions need to have parallel producers with the Mustache inputs)

39be31f fixes the bug mentioned in the second bullet of @slava77's review report in https://github.com/cms-sw/cmssw/pull/1242