prefetch does not provide abundance information in CSV outputs

[bluegenes]

prefetch flattens abundances by default when searching (intended). But it would be good to reinflate abundances before saving matched and unmatched sigs, to keep abundances around.

Note that this means any downstream gather steps using the matches.sig, as the query currently ignore abundance by default. When abundances are added, these gathers will use abundances again unless --ignore-abundance is specified.