[CppAD] Pow function doesn't work with double exponent

[Mitch Watrous]

Hi.

I would like the pow function to be modified so that it works for the case

    pow( WT, 0.425 )

where WT is of

     Type = CppAD::AD<CppAD::AD<CppAD::AD<double> > >


Thanks,
Mitch Watrous
RFPK
University of Washington