[Rd] pt not monotonic with large noncentrality (PR#14069)

[Jerry.Lewis at biogenidec.com]

Full_Name: Jerry W. Lewis
Version: 2.10.0
OS: Windows XP Professional
Submission from: (NULL) (96.237.55.233)


pt(0,3,200)      # correctly returns 0
pt(-1000,3,200)  # erroniously returns 0.003116595

Since pt(0,df,nc) = pnorm(-nc), there is an easily computed upper bound for
pt(-t,df,nc) where t>0 and nc>0.