[SPARK-1570] Fix classloading in JavaSQLContext.applySchema

I think I hit a class loading issue when running JavaSparkSQL example using spark-submit in local mode.

Author: Kan Zhang <kzhang@apache.org>

Closes #484 from kanzhang/SPARK-1570 and squashes the following commits:

feaaeba [Kan Zhang] [SPARK-1570] Fix classloading in JavaSQLContext.applySchema