added discriminative type to grammar
updated parser.parse_update_schema for descriminative types, not implemented in engine
Added fix to PLOT SELECT - key column should be dropped from the query output before plotting
First steps toward subsampling. Need to test still.
Fix subsampling
Merge branch 'subsample'
Merge branch 'master' into discrim
Merge remote-tracking branch 'remotes/origin/discriminitive_parsing' into discrim

Conflicts:
	bayesdb/engine.py