special/cephes/hyp2f1: improve accuracy for |a|, |b| > |c| by using recurrence relations
special/cephes/hyp2f1: improve accuracy for |a|, |b| > |c| by using recurrence relations

The hypergeometric series may become highly alternating when |a| or |b| >> |c|
and some of the quantities involved is negative. This can be worked
around by using hypergeometric recurrence relations to reduce the
magnitude of |a| closer to that of |c|.

git-svn-id: 003f22d385e25de9cff933a5ea4efd77cb5e7b28@6047 d6536bca-fef9-0310-8506-e4c0a848fbcf

jasonmccampbell/scipy-refactor,scipy/scipy-svn,jasonmccampbell/scipy-refactor,jasonmccampbell/scipy-refactor,lesserwhirls/scipy-cwt,jasonmccampbell/scipy-refactor,lesserwhirls/scipy-cwt,lesserwhirls/scipy-cwt,lesserwhirls/scipy-cwt,scipy/scipy-svn,scipy/scipy-svn,scipy/scipy-svn