Complex arg-trig functions

[Stephen Montgomery-Smith]

1. Your recent optimizations seem to have given an overall 3% time 
saving in my timing tests.  That's pretty good in my opinion.

2.  In my accuracy tests for casin(h), I have never seen the double or 
long double have an error greater than 4 ULP.  But for the float case I 
have seen 4.15 ULP.

3.  I saw that you have ideas on making catanh have an error less than 1 
ULP.  Just saying that I saw those comments, although I didn't read them 
very carefully.