Modified sphere.f90 to be consistent with Bruce Draine's 'adt.f' code. Catches a zero-valued real component of m-1, and uses an approximation for when rho << 1.
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Edited sphere.f90 module to reflect a discovered mistake in equation (16) (extinction efficiency for spheres) from Draine & Allaf-Akbari 2006. When Re(m-1) > 0, the old expression produced physically implausible results (i.e., negative efficiencies, efficiencies greater than 2). By changing the sign of |rho|sin(Re(rho) - beta) when Re(m-1) > 0, the result is consistent with Mie theory. Derivations of the correct formula are in progress.