updated to most recent SourceTracker release

this includes some changes that will facilitate use with QIIME 1.7.0
modified env variable that gets set
Merge pull request #50 from gregcaporaso/st-0.9.5

updated to pull SourceTracker 0.9.5
Updated qiime-1.6.0-dev/qiime.conf and picrust-0.9.0-dev/picrust.conf to install R 2.12.2
Merge pull request #51 from dmdu/install_r_2.12.2

Updated qiime-1.6.0-dev/qiime.conf to install R 2.12.2
Reverted R version back to 2.12.0 for now.

PICRUSt and QIIME builds are often hanging indefinitely, and after discussing with @gregcaporaso, we decided to revert for now since we have a QIIME release on Monday. We can then look into the failures and upgrade the version after the release.

I'll do a bit more debugging on my end and post details in a separate issue.
Merge pull request #52 from jrrideout/r_version_revert

Reverted R version back to 2.12.0 for now.