fix missing last flow/substance record

[fenclmar]

The last record of inflow was not considered in pumping as pumping is 'one step behind' inflow. V and S vectors are extended and one more loop added. In addition, flow volume left in a pump sump after pumping was added into flow object as a new attribute to enable better testing of mass balance. Here there is a test of the fixed function:

Q <- rep(10, 100) + rnorm(100,0,1)
Q <- data.frame('Q' = Q, 'S' = Q * .01)
attr(Q, "temp.res.sim") <- 60
plot(Q[ ,1], type='l')
V = sum(Q[ ,1])*60
Qout <- pump.trans(Q, 7777, 0, 23)
V2 <- sum(Qout[ ,1]) * 60 + attr(Qout, "V.in.sump")
print(V)
print(V2)