[Halld-offline] selection of p pi+ pi-, p pi+ pi- pi0 events

[Kei Moriya]

I've updated the code to select specific reactions.
The files are in
trunk/sim-recon/src/programs/Utilities/hddm_select_events

You can run on non-REST files with
hddm_select_events -s 5 -i [input hddm] -o [output hddm]
To run over REST files use the -r option.
The option -s [selectType] specifies which events you
want to select. 5 is for p pi+ pi-, 6 is for p pi+ pi- pi0.

If people could give me comments on why I don't get
exactly the same number of events when running with
different EM backgrounds, I would be grateful.

	Kei