math related suggestions

[Pavel Demin]

Looking at the Delphes code, I've noticed a couple of things that could be improved:

• Most of the underlying libraries operate with double precision numbers. However in Delphes, some variables are single precision. Should not we switch to double for all variables?
• There are at least 13 calls to something like sqrt(pow(x,2), pow(y,2)). As most of them are inside loops, it would be better to replace them with hypot(x, y). Here is a command to find corresponding lines:

  grep -r "sqrt( *pow" trunk/* | grep c: