Altered TR's random arithmetic testing to generate single-flonums and very small flonums; fails now because of erroneous types
Fixes to sgn, sinh, cosh, and tanh:
* preserve single-flonum-ness
* correct zero sign (-0.0) for negative return values that are smaller than epsilon
* correct behavior with NaN and infinite inputs
This makes it more efficient to plot piecewise functions by drawing each piece with one renderer, and possible to plot functions with discontinuities by using a renderer to draw each continuous piece.
