[Gemc_software] hit sharing

[Maurizio Ungaro]

Hi all,

I just committed a change in gemc that allows the creation of several hits from a single geant4 step.
As a reminder, until now only the opposite was true: a track could have several steps in the same drift chamber cell for example. At max, we could have 1 hit per step.

Now one could have several hit for a single step. This is useful for example for phenomena such as charge sharing on silicon strip detectors.

No changes are required from users,  and this change is backward compatible. To use this feature, users can use the already existing identifiers routines. 
For example, this is how it works on SVT:

	strip_id.push_back(ClosestStrip);
	strip_id.push_back(0.45);
	strip_id.push_back(ClosestStrip+1);
	strip_id.push_back(0.45);
		
so in this case you can see that 2 strips are hit, and the energy deposited will be weighted by 0.45 for each strip.
You can add as many hits as you want per step. 

Just a reminder: the hit weight is not checked internally by gemc, so make sure you know what you're doing.
In other words, if one put 0.9 instead of 0.45 in the example above, one would wrongly create 80% of additional "fake" energy.

Please let  me know if you have any questions or issues.

sincerely,
mauri