Removed reference to incubation in Spark user docs.

Author: Reynold Xin <rxin@apache.org>

Closes #2 from rxin/docs and squashes the following commits:

08bbd5f [Reynold Xin] Removed reference to incubation in Spark user docs.
Remote BlockFetchTracker trait

This trait seems to have been created a while ago when there
were multiple implementations; now that there's just one, I think it
makes sense to merge it into the BlockFetcherIterator trait.

Author: Kay Ousterhout <kayousterhout@gmail.com>

Closes #39 from kayousterhout/remove_tracker and squashes the following commits:

8173939 [Kay Ousterhout] Remote BlockFetchTracker.
SPARK-1032. If Yarn app fails before registering, app master stays aroun...

...d long after

This reopens https://github.com/apache/incubator-spark/pull/648 against the new repo.

Author: Sandy Ryza <sandy@cloudera.com>

Closes #28 from sryza/sandy-spark-1032 and squashes the following commits:

5953f50 [Sandy Ryza] SPARK-1032. If Yarn app fails before registering, app master stays around long after
SPARK-1051. On YARN, executors don't doAs submitting user

This reopens https://github.com/apache/incubator-spark/pull/538 against the new repo

Author: Sandy Ryza <sandy@cloudera.com>

Closes #29 from sryza/sandy-spark-1051 and squashes the following commits:

708ce49 [Sandy Ryza] SPARK-1051. doAs submitting user in YARN
SPARK-1151: Update dev merge script to use spark.git instead of incubator-spark

Author: Thomas Graves <tgraves@apache.org>

Closes #47 from tgravescs/fix_merge_script and squashes the following commits:

8209ab1 [Thomas Graves] Update dev merge script to use spark.git instead of incubator-spark
[SPARK-979] Randomize order of offers.

This commit randomizes the order of resource offers to avoid scheduling
all tasks on the same small set of machines.

This is a much simpler solution to SPARK-979 than #7.

Author: Kay Ousterhout <kayousterhout@gmail.com>

Closes #27 from kayousterhout/randomize and squashes the following commits:

435d817 [Kay Ousterhout] [SPARK-979] Randomize order of offers.
[SPARK-1150] fix repo location in create script

https://spark-project.atlassian.net/browse/SPARK-1150

fix the repo location in create_release script

Author: Mark Grover <mark@apache.org>

Closes #48 from CodingCat/script_fixes and squashes the following commits:

01f4bf7 [Mark Grover] Fixing some nitpicks
d2244d4 [Mark Grover] SPARK-676: Abbreviation in SPARK_MEM but not in SPARK_WORKER_MEMORY
Revert "[SPARK-1150] fix repo location in create script"

This reverts commit 9aa095711858ce8670e51488f66a3d7c1a821c30.
[SPARK-1150] fix repo location in create script (re-open)

reopen for https://spark-project.atlassian.net/browse/SPARK-1150

Author: CodingCat <zhunansjtu@gmail.com>

Closes #52 from CodingCat/script_fixes and squashes the following commits:

fc05a71 [CodingCat] fix repo location in create script
[SPARK-1100] prevent Spark from overwriting directory silently

Thanks for Diana Carroll to report this issue (https://spark-project.atlassian.net/browse/SPARK-1100)

the current saveAsTextFile/SequenceFile will overwrite the output directory silently if the directory already exists, this behaviour is not desirable because

overwriting the data silently is not user-friendly

if the partition number of two writing operation changed, then the output directory will contain the results generated by two runnings

My fix includes:

add some new APIs with a flag for users to define whether he/she wants to overwrite the directory:
if the flag is set to true, then the output directory is deleted first and then written into the new data to prevent the output directory contains results from multiple rounds of running;

if the flag is set to false, Spark will throw an exception if the output directory already exists

changed JavaAPI part

default behaviour is overwriting

Two questions

should we deprecate the old APIs without such a flag?

I noticed that Spark Streaming also called these APIs, I thought we don't need to change the related part in streaming? @tdas

Author: CodingCat <zhunansjtu@gmail.com>

Closes #11 from CodingCat/SPARK-1100 and squashes the following commits:

6a4e3a3 [CodingCat] code clean
ef2d43f [CodingCat] add new test cases and code clean
ac63136 [CodingCat] checkOutputSpecs not applicable to FSOutputFormat
ec490e8 [CodingCat] prevent Spark from overwriting directory silently and leaving dirty directory