====== Revert particle ID to a positive number in DecayTreeTuple ======
===== Idea =====
It may sometimes be useful to store particles always under the same label, for instance always as ''muminus'' and not as ''muplus'' and ''muminus'' in the nTuple. This will allow to chain or merge the root files in an easy way afterwards. A simple example may be:

<code>
Tuple = DecayTreeTuple("MisID")
Tuple.InputLocations = ["Phys/StdNoPIDsMuons"]
Tuple.Decay = "[mu+]cc"
</code>

which takes every particle, assigns it the ID of a muon / antimuon, and saves it in the tuple. The problem here exactly is that the files can't be merged afterwards.

===== How to =====
If you have something like
<code>
myTuple = DecayTreeTuple("myTuple")
</code>
add
<code>
myTuple.RevertToPositiveID = True
</code>
which will do the job.