[SPARK-4422][MLLIB]In some cases, Vectors.fromBreeze get wrong results.

cc mengxr

Author: GuoQiang Li <witgo@qq.com>

Closes #3281 from witgo/SPARK-4422 and squashes the following commits:

5f1fa5e [GuoQiang Li] import order
50783bd [GuoQiang Li] review commits
7a10123 [GuoQiang Li] In some cases, Vectors.fromBreeze get wrong results.

(cherry picked from commit 5168c6ca9f0008027d688661bae57c28cf386b54)
Signed-off-by: Xiangrui Meng <meng@databricks.com>
[SPARK-4410][SQL] Add support for external sort

Adds a new operator that uses Spark's `ExternalSort` class.  It is off by default now, but we might consider making it the default if benchmarks show that it does not regress performance.

Author: Michael Armbrust <michael@databricks.com>

Closes #3268 from marmbrus/externalSort and squashes the following commits:

48b9726 [Michael Armbrust] comments
b98799d [Michael Armbrust] Add test
afd7562 [Michael Armbrust] Add support for external sort.

(cherry picked from commit 64c6b9bad559c21f25cd9fbe37c8813cdab939f2)
Signed-off-by: Reynold Xin <rxin@databricks.com>
Revert "Preparing development version 1.2.1-SNAPSHOT"

This reverts commit 6c6fd218c83a049c874b8a0ea737333c1899c94a.
Revert "Preparing Spark release v1.2.0-snapshot0"

This reverts commit bc09875799aa373f4320d38b02618173ffa4c96f.
Preparing Spark release v1.2.0-snapshot1
Preparing development version 1.2.1-SNAPSHOT