Format of selected particle ID1 and ID2

Just a reminder for the use of the selected particles with ID1 and ID2.

From Andreas's email:

the ID1 and ID2 are in the format (x,y,z,px,py,pz) this is different than in the case when you read from file. 

A coherent format for ID1 and ID2 with the distribution from file would be nicer, as well as a unique definition of the longitudinal momentum between OPAL-T and OPAL-Cyc. At the moment, they differ not only in used variable (pz for OPAL-T and py for OPAL-Cyc) but also in the meaning:

• pz in OPAL-T indicates the longitudinal momentum of the particle,
• py in OPAL-Cyc indicates the momentum offset with respect to the reference momentum