add doSNOW to Suggests

git-svn-id: https://hedgehog.fhcrc.org/bioconductor/trunk/madman/Rpacks/VanillaICE@72779 bc3139a8-67e5-0310-9ffc-ced21a209358
import iterators
fix crlmmDownstream vignette
add iterators to imports

git-svn-id: https://hedgehog.fhcrc.org/bioconductor/trunk/madman/Rpacks/VanillaICE@72807 bc3139a8-67e5-0310-9ffc-ced21a209358