add code to test data
bugfix --- correct yb generation for channel

I wonder why this didn't come up before...
introduce switches for different datasets

test_interp now has switches, and it will only test the datasets that
are requested.
bugfix --- actually use the nmax and mmax values

i.e. don't kill my computer trying to compute all the many neighbour
channel flow polynomials
add message at interpolate_spline start

since this can take a while, perhaps people would like to see some sign
that something is happening.
Merge branch 'issue#2' into develop