Extensive use of abs for complex tolerances

[weymouth]

I just profiled expintx(1,z::Complex) and found the majority of the time is spent checking the convergence using abs(stuff) < ϵ. Would there be a problem with simply squaring all of these and using abs2(stuff) < ϵ^2? This is much much faster, especially when stuff::Complex.

Since ϵ=10eps(T), I suppose that could lead to some issues. But I would much prefer to slightly reduce the tolerance than the current waste of compute.

I'm happy to do the PR if it's likely to get merged in.

[weymouth]

Or we could just use fastabs. That should be harmless, right?

[stevengj]

Yes, fastabs should be fine here. Not sure how that compares to abs2, but with abs2 you also need to be careful of over/underflow.