regression in eigs

[c.]

Hi,

I just found a nasty regression in eigs when a numerical value is provided
and the size of the matrix / number of eigenvalues cause a fallback to eig

I think the fix is trivial so it is worth doing before the release, but I 
don't have time to do it until this evening, so I just pushed a failing test
to show the problem for the moment.

I'll push the fix later today if no one does it before me.

c.