Corrections to adjoint of npzd_iron.h and npzd_Powell.h

[arango]

Several corrections were made to tl_npzd_iron.h, rp_npzd_iron.h, and ad_npzd_iron.h. These routines now pass the sanity checks and Picard iterations test. Many thanks to Andy Moore for making these corrections and Jerome Fiechter for carrying out the test.

I also corrected the light formulation in tl_npzd_Powell.h, rp_npzd_Powell.h, and ad_npzd_Powell.h. This new formulation was not correctly adjointed.