[Rd] prcomp need Conj(t(s$vt)) (PR#2924)

[pgilbert at bank-banque-canada.ca]

In prcomp

        s <- La.svd(x, nu = 0)
        s$v <- t(s$vt)

the second above line should be 

        s$v <- Conj(t(s$vt))

(to cover complex cases).

Paul Gilbert