Override getParameters for main

[anigamova]

Same as #903, provide a fix for discrete profiling in root v6.26

[guitargeek]

Thanks for this! There are some issues with it still:

• the added function leaks memory (the return value of the getParameters called internally)
• the fix also needs to be applied to CachingAddNLL
• it's a bit risky to overload both the old and new getParameters signature at the same time. Depending on how ROOT implements things, there might be infinite recursion

All this this is not your fault: I should have been more careful when changing interfaces, and combine should have used the override keyword like the rest of CMSSW to catch this early.

Sustainable fix proposed in: https://github.com/cms-analysis/HiggsAnalysis-CombinedLimit/pull/948

[anigamova]

Thanks @guitargeek for looking into this and providing a better fix for this issue. We'll test the changes from #948 and hopefully merge it soon