[Primexd] Random trigger skims

[Alexander Austregesilo]

Hi Igal,

We have a plugin called randomtrigger_skim to filter out the random 
triggers from any evio input and convert them into the hddm format that 
can be mixed into the simulation by mcsmear. To be more realistic, we 
only accept random triggers that fall into a time period were the beam 
was actually on. The plugin takes this beam fiducial map into account, 
but it has to be generated beforehand. Peter Pauli (cc) was just working 
on an improved scheme for this extraction, maybe he can help you also 
for the PrimEx data.

Once the fiducial map is ready, you just have to run the plugin over all 
evio files. Afterwards, we can concatenate the hddm skims from 
individual evio files so that we have one file per run.

Before you have the fiducial map, you can also include the option 
`RANDSKIM:USEBEAM 0` into your config file to simply write out all 
random triggers. This serves already as a good approximation.

Let me know if you have any questions,

Alex