v1.3.20 mod assignment methods to account for refseq
v1.3.20 revised some phyloseq infrastructure

Needs testing, more revisions to go.
prune_samples needs testing, further mod
- prune_* / reconcile_* / intersect_*
	- add intersect_samples() function, model after new version of
intersect_species()
	- rename intersect_species to intersect_taxa()
	- revise prune_samples, reuse intersect_samples
	- rm/replace reconcile_* functions with prune_*(intersect_*(), ps).
That's all it's doing now.
	- These changes make simpler / DRYer code. Easier to extend.