Updated programming-guide.md

Made sure that readers know the random number generator seed argument, within the 'takeSample' method, is optional.

Author: Rishi Verma <riverma@apache.org>

Closes #1324 from riverma/patch-1 and squashes the following commits:

4699676 [Rishi Verma] Updated programming-guide.md
Resolve sbt warnings during build Ⅱ

Author: witgo <witgo@qq.com>

Closes #1153 from witgo/expectResult and squashes the following commits:

97541d8 [witgo] merge master
ead26e7 [witgo] Resolve sbt warnings during build
[SPARK-2391][SQL] Custom take() for LIMIT queries.

Using Spark's take can result in an entire in-memory partition to be shipped in order to retrieve a single row.

Author: Michael Armbrust <michael@databricks.com>

Closes #1318 from marmbrus/takeLimit and squashes the following commits:

77289a5 [Michael Armbrust] Update scala doc
32f0674 [Michael Armbrust] Custom take implementation for LIMIT queries.
[EC2] Add default history server port to ec2 script

Right now I have to open it manually

Author: Andrew Or <andrewor14@gmail.com>

Closes #1296 from andrewor14/hist-serv-port and squashes the following commits:

8895a1f [Andrew Or] Add default history server port to ec2 script