fix manual thresholds, output values, to known true

Ran the coloc_2 on the positive correlation test images
colocsample1b-green.tif ch1, -red ch2, using the mask image we use
here, colocsample1b-mask.tif to find the auto thresholds (bisection
method) generated and thresholded Manders' coefficients resulting.
Then hard code these into this unit test. Set the precision of the test
to be a very precise 0.000001, so that it will fail if any tiny
disturbances/bugs happen elsewhere numerically or with faulty logic or
maths. Hopefully this makes the test much more robust at catching
problems that the other test here that works on the artificial smooth
images fro the Manders paper with no thresholds.