TST: accept small error in threaded random test

freebsd and windows change x87 precision mode (fctrl bit 8 and 9) from
extended to double in child threads so the random numbers cannot be
exactly the same from master and child threads.
see gh-4909

Pep8 numpy random

This is in numpy/random/mtrand/mtrand.pyx where the choice function
was using comparisons of the form `None != p`.

closes gh-4526

-- Addresses https://github.com/numpy/numpy/issues/4763

rho results in 0. for kappa < 1.4e-8 whch leads to nans appearing and an
infinite loop.
the second order taylor expansion is more precise up to at least 1e-5.
Closes gh-4720

mtrand accepts seeds larger than 32 bit but silently truncates them back
to 32 bit. This can lead to accidentally getting the same random stream
for two different seeds, e.g. 1 and 1 + 2**40.