Squishing a typo bug before it causes real harm

in updateNumRows method in RowMatrix

Author: Doris Xin <doris.s.xin@gmail.com>

Closes #1125 from dorx/updateNumRows and squashes the following commits:

8564aef [Doris Xin] Squishing a typo bug before it causes real harm

(cherry picked from commit 566f70f2140c1d243fe2368af60ecb390ac8ab3e)
Signed-off-by: Xiangrui Meng <meng@databricks.com>
[SPARK-2187] Explain should not run the optimizer twice.

@yhuai @marmbrus @concretevitamin

Author: Reynold Xin <rxin@apache.org>

Closes #1123 from rxin/explain and squashes the following commits:

def83b0 [Reynold Xin] Update unit tests for explain.
a9d3ba8 [Reynold Xin] [SPARK-2187] Explain should not run the optimizer twice.

(cherry picked from commit 640c294369f49a7602c33c7c389088aec8a316d3)
Signed-off-by: Reynold Xin <rxin@apache.org>