BUG: special: ellip(k,e)inc nan and double expected value

Both ellipkinc and ellipeinc returned nan for a particular value
due to cancelation in a tangent update formula.  Double the
expected value was returned in a small region around the value
returning nan due to using a fragile argument reduction formula.

Fixes gh-3550
Merge pull request #3704 from ewmoore/ellik_fix

BUG: special: ellip(k,e)inc nan and double expected value