[SPARK-1644] The org.datanucleus:* should not be packaged into spark-assembly-*.jar

Author: witgo <witgo@qq.com>

Closes #688 from witgo/SPARK-1644 and squashes the following commits:

56ad6ac [witgo] review commit
87c03e4 [witgo] Merge branch 'master' of https://github.com/apache/spark into SPARK-1644
6ffa7e4 [witgo] review commit
a597414 [witgo] The org.datanucleus:* should not be packaged into spark-assembly-*.jar
[SQL] Upgrade parquet library.

I think we are hitting this issue in some perf tests: https://github.com/Parquet/parquet-mr/commit/6aed5288fd4a1398063a5a219b2ae4a9f71b02cf

Credit to @aarondav !

Author: Michael Armbrust <michael@databricks.com>

Closes #684 from marmbrus/upgradeParquet and squashes the following commits:

e10a619 [Michael Armbrust] Upgrade parquet library.
[SPARK-1778] [SQL] Add 'limit' transformation to SchemaRDD.

Add `limit` transformation to `SchemaRDD`.

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #711 from ueshin/issues/SPARK-1778 and squashes the following commits:

33169df [Takuya UESHIN] Add 'limit' transformation to SchemaRDD.