[Rd] chi-squared with zero df (PR#10551)

[Jerry.Lewis at biogenidec.com]

Full_Name: Jerry W. Lewis
Version: 2.6.1
OS: Windows XP Professional
Submission from: (NULL) (24.147.191.250)


pchisq(0,0,ncp=lambda) returns 0 instead of exp(-lambda/2)

pchisq(x,0,ncp=lambda) returns NaN instead of exp(-lambda/2)*(1 +
SUM_{r=0}^infty ((lambda/2)^r / r!) pchisq(x, df + 2r))

qchisq(.7,0,ncp=1) returns 1.712252 instead of 0.701297103

qchisq(exp(-1/2),0,ncp=1) returns 1.238938 instead of 0