[Developers] incomplete beta function is broken

[dave fournier]

As I noted earlier the cephes version of the beta (and probably  log 
gamma) functions
appear to lack sufficient smoothess for the random effects stuff.    The 
solution is to go
back to the versions based on NR.  However rather than replacing them I 
think it would be
easier to simply add the old functions to the package with a slight name 
change.
Could use capitals as Betai, Gammln. Then both versions would be 
available and
experience would show which are best for various applications.  Any 
thoughts?