incomplete sentences, timings, removed gg download

Fixed some issues, making the call to ``validate_mapping_file.py``, added a approx. timing mention to ``pick_open_reference_otus.py`` and most notably removed the download for greengenes. The untar'ing on EC2 instances is brutal, and these data should be staged anyway in the instance (though not sure if this is the case with the QIIME AMIs)