Bug#916292: Kahan summation not working on i386

[Jerome Kieffer]

Hi,

This FBFS bug comes down to the POCL on i386 which is not able to
perform calculation as described by the OpenCL spec.

It is likely a numerical optimization at the wrong place as those tests
ensures the calculation are performed as expected.
This is described in:
https://en.wikipedia.org/wiki/Kahan_summation_algorithm#Possible_invalidation_by_compiler_optimization

If I find some time I could have a look at it, but on the other hand, pyFAI does
not support 32bits architecture as it requires often more than 2GB of memory
for real scientific application.

-- 
Jérôme Kieffer: core dev of pyFAI.