erge branch 'master' of https://github.com/biocore/qiime into remote

updating to more recent version of qiime
Merge branch 'master' of https://github.com/biocore/qiime into add-swarm

merge latest changes from upstream master
added swarm
code review modifications + change of using 'uclust_otu_prefix_id' to 'denovo_otu_prefix_id' & all de novo tools
Merge pull request #1643 from ekopylova/add-swarm

Add swarm to pick_otus.py