layerpot eval should use @utils/fundsol for radial derivatives

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Currently S,D,T kernel evaluations in @layerpot use the old fundsol and
fundsol_deriv codes (when opts.fast=0). They should be phased out in favor
of @utils/fundsol. The complication will be that the old fundsol_deriv
included computing (or having passed in) the cosine-phi factors, and this
will have to be explicitly coded since the new fundsol only computes radial
derivative.
This is largely moot for opts.fast=1,2 since then Rokhlin routines are
called directly (however fundsol_deriv is still used to compute cosine-phi,
clumsily).

Original issue reported on code.google.com by [email protected] on 21 Jul 2009 at 5:14