[Rd] "integrate" error using a constant function (PR#8348)

[joelpf@u.washington.edu]

Full_Name: Joel Franklin
Version: 2.2.0
OS: WinXP-Prof
Submission from: (NULL) (63.226.223.22)


The "integrate" function, when evaluating an integrand function that is constant
(therefore not a function of the integral) cannot be valuated, and instead
throws an error. Instead, the interate function should evaluate the constant
function as a rectangular area with length (upper-lower).

For example:

integrand<-function(x){5}
integrate(f=integrand,lower=1,upper=5)

"Error in integrate(f = integrand, lower = 1, upper = 5) : 
        evaluation of function gave a result of wrong length"