[Ifeffit] care and feeding of Athena

[Matt Newville]

Hi Bruce, All,

These issues are almost certainly due to some bug in Ifeffit that gets
triggered with large data sets.  As Bruce mentioned, Ifeffit
internally keeps track of arrays and groups using a built-in memory
cache.  By trying to write portable Fortran, this was more-or-less a
requirement (at least, it was several years ago when Ifeffit was first
being written).

I have a few tests for moving arrays around that pass for me without
any trouble, but there are definitely occasional problems with "large
sets of data" -- I've seen these myself.    Unfortunately, I don't
have a good simple test case that always causes a problem.   If you
have a project file that is "acting weird"  and data is clearly being
corrupted, please send it to me.

--Matt