evp.solvespectrum method 'fd' should treat degeneracies better

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Since 'fd' is the premier method for low eigenvalues, should identify 
degeneracies closer than sqrt(eps) (?) and handle separately using local search 
('fd' or 'ms'?)
to try and regain accuracy close to eps.

Currently accuracy limited to sqrt(eps), ie 1e-8, by the Boyd analytic 
rootfinder.

Original issue reported on code.google.com by [email protected] on 21 Dec 2011 at 5:04