MLlib documentation fix

Synchronized mllib-optimization.md with Spark Scaladoc: removed reference to GradientDescent.runMiniBatchSGD method

This is a temporary fix to remove  a link from http://spark.apache.org/docs/latest/mllib-optimization.html to GradientDescent.runMiniBatchSGD which is not in the current online GradientDescent Scaladoc.
FIXME: revert this commit after GradientDescent Scaladoc is updated.
See images for details.

![mllib-docs-fix-1](https://cloud.githubusercontent.com/assets/1375501/3294410/ccf19bb8-f5a8-11e3-93f1-f593016209eb.png)
![mllib-docs-fix-2](https://cloud.githubusercontent.com/assets/1375501/3294411/d0b59a7e-f5a8-11e3-8fc8-329c177ef8c8.png)

Author: Anatoli Fomenko <fa@apache.org>

Closes #1098 from afomenko/master and squashes the following commits:

5cb0758 [Anatoli Fomenko] MLlib documentation fix

(cherry picked from commit 7afa912e747c77ebfd10bddf7bda2e3190fdeb9c)
Signed-off-by: Xiangrui Meng <meng@databricks.com>
SPARK-1990: added compatibility for python 2.6 for ssh_read command

https://issues.apache.org/jira/browse/SPARK-1990

There were some posts on the lists that spark-ec2 does not work with Python 2.6. In addition, we should check the Python version at the top of the script and exit if it's too old

Author: Anant <anant.asty@gmail.com>

Closes #941 from anantasty/SPARK-1990 and squashes the following commits:

4ca441d [Anant] Implmented check_optput withinthe module to work with python 2.6
c6ed85c [Anant] added compatibility for python 2.6 for ssh_read command

Conflicts:

	ec2/spark_ec2.py
[SPARK-2144] ExecutorsPage reports incorrect # of RDD blocks

This is reproducible whenever we drop a block because of memory pressure.

This is because StorageStatusListener actually never removes anything from the block maps of its StorageStatuses. Instead, when a block is dropped, it sets the block's storage level to `StorageLevel.NONE`, when it should just remove it from the map.

This PR includes this simple fix.

Author: Andrew Or <andrewor14@gmail.com>

Closes #1080 from andrewor14/ui-blocks and squashes the following commits:

fcf9f1a [Andrew Or] Remove BlockStatus if it is no longer cached
(cherry picked from commit 09deb3eee090eb8ec1d9a0cd90825699748e3ffc)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>