single end hits

[Blake Leverington <leverinb@uregina.ca>]

Hey all,

So a question before I start trying to implement single ended hits into 
the bcal code, is there any reason that there has to be 2-ended hits 
such as some catastrophic error or is it just that a few things aren't 
able to be calculated for those hits, such as z and t or just need to be 
calculated differently, like e? I'm referring to the variables in 
DBCALShower_factory. I have a general idea how to go about this, and it 
seems fairly simple, but I was just checking to make sure there isn't 
anything down the line that will be affected that people are aware of.

-Blake