SPARK-1611: Fix incorrect initialization order in AppendOnlyMap

JIRA: https://issues.apache.org/jira/browse/SPARK-1611

Author: zsxwing <zsxwing@gmail.com>

Closes #534 from zsxwing/SPARK-1611 and squashes the following commits:

96af089 [zsxwing] SPARK-1611: Fix incorrect initialization order in AppendOnlyMap
(cherry picked from commit 78a49b2532d4751257654dfe55a564bcd10701b3)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>
Spark 1490 Add kerberos support to the HistoryServer

Here I've added the ability for the History server to login from a kerberos keytab file so that the history server can be run as a super user and stay up for along period of time while reading the history files from HDFS.

Author: Thomas Graves <tgraves@apache.org>

Closes #513 from tgravescs/SPARK-1490 and squashes the following commits:

e204a99 [Thomas Graves] remove extra logging
5418daa [Thomas Graves] fix typo in config
0076b99 [Thomas Graves] Update docs
4d76545 [Thomas Graves] SPARK-1490 Add kerberos support to the HistoryServer
(cherry picked from commit bd375094a1480b0ff9c16ab8ddd2dba8731506df)

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