[Ifeffit] residual in non-equally spaced data

[Matt Newville]

Hi Francesco,

Yes, I believe that Artemis calculates the residual
incorrectly for chi(k) data which is not on the strictly
uniform k-grid [0.0,0.05,0.10,...] Ang^-1.

Ifeffit does the fit correctly (it internally interpolates
the data to the uniform grid), and writes the best-fit
result with this k-grid (and this is a feature, not a
bug).   Artemis calculates the residual itself,   and
doesn't  check if the k-array for data and fit match.

Sorry for the trouble, and hope that helps.   Both
Bruce and I have been swamped with other work
the last year or so that such bug fixes take a lot of
time to get fully resolved and released.

--Matt