[SPARK-4652][DOCS] Add docs about spark-git-repo option

There might be some cases when WIPS spark version need to be run
on EC2 cluster. In order to setup this type of cluster more easily,
add --spark-git-repo option description to ec2 documentation.

Author: lewuathe <lewuathe@me.com>
Author: Josh Rosen <joshrosen@databricks.com>

Closes #3513 from Lewuathe/doc-for-development-spark-cluster and squashes the following commits:

6dae8ee [lewuathe] Wrap consistent with other descriptions
cfaf9be [lewuathe] Add docs about spark-git-repo option

(Editing / cleanup by Josh Rosen)
[SPARK-4397] Move object RDD to the front of RDD.scala.

I ran into multiple cases that SBT/Scala compiler was confused by the implicits in continuous compilation mode. Adding explicit return types fixes the problem.

Author: Reynold Xin <rxin@databricks.com>

Closes #3580 from rxin/rdd-implicit and squashes the following commits:

ee32fcd [Reynold Xin] Move object RDD to the end of the file.
b8562c9 [Reynold Xin] Merge branch 'master' of github.com:apache/spark into rdd-implicit
d4e9f85 [Reynold Xin] Code review.
a836a37 [Reynold Xin] Move object RDD to the front of RDD.scala.
[SPARK-4421] Wrong link in spark-standalone.html

Modified the link of building Spark.

Author: Masayoshi TSUZUKI <tsudukim@oss.nttdata.co.jp>

Closes #3279 from tsudukim/feature/SPARK-4421 and squashes the following commits:

56e31c1 [Masayoshi TSUZUKI] Modified the link of building Spark.
Fix typo in Spark SQL docs.

Author: Andy Konwinski <andykonwinski@gmail.com>

Closes #3611 from andyk/patch-3 and squashes the following commits:

7bab333 [Andy Konwinski] Fix typo in Spark SQL docs.
[SPARK-4464] Description about configuration options need to be modified in docs.

Added description about -h and -host.
Modified description about -i and -ip which are now deprecated.
Added description about --properties-file.

Author: Masayoshi TSUZUKI <tsudukim@oss.nttdata.co.jp>

Closes #3329 from tsudukim/feature/SPARK-4464 and squashes the following commits:

6c07caf [Masayoshi TSUZUKI] [SPARK-4464] Description about configuration options need to be modified in docs.