Resolve "TQMultiObservable should lazily evaluate subObservables"

Release notes

Lazy evaluation of components in TQMultiObservable: if using Root >6.06 (i.e. Rel21+) TQMultiObservable now only evaluates subobservables when really needed. This allows, e.g., for easier handling of quantities that are only defined under certain conditions like DYjj requiring at least two jets in the event. For example the expression '[nJets]>1 ? [DYjj] : -999.' will only evaluate the DYjj observable if the value of the nJets observable is >1 for the respective event.

Details

see issue closed by this MR. Also note again that this only affects things when compiling against ROOT 6.06+ as the TFormula constructor needed to make this work was only introduced in 6.06!

Closes #162 (closed)

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• c3ecea20 - first implementation of lazily evaluated subObservables
• 63abfc13 - removing commented segments no longer needed

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• e77332a6 - slight compiler soothing (preventing a warning)

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• d1363bec - adding old code back in (with root version switch) to fix compillation in Root 6.04

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assigned to @rgugel

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• 2e870892 - donot compile expression again after parsing in TQMultiObservable

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• 87dd5673 - compillation fixes

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• c42c009a - typo

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• c42c009a...a884955d - 48 commits from branch master
• 2b9d69d3 - Merge remote-tracking branch 'origin/master' into…

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mentioned in issue #171

merged

mentioned in commit 91d3adaf

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