Allow latest scala in PATH, with SCALA_HOME as override (instead of vice-versa)

Update wording of section on RDD operations in quick start guide in docs

Reversed the order of tests to find a scala executable (in the case when SPARK_LAUNCH_WITH_SCALA is defined): instead of checking in the PATH first, and only then (if not found) for SCALA_HOME, now we check for SCALA_HOME first, and only then (if not defined) do we look in the PATH.  The advantage is that now if the user has a more recent (non-compatible) version of scala in her PATH, she can use SCALA_HOME to point to the older (compatible) version for use with spark.

Suggested by Josh Rosen in this thread:

  https://groups.google.com/forum/?fromgroups=#!topic/spark-users/NC9JKvP8808

Add details when BlockManager heartbeats time out

Makes it more clear what the threshold was for tuning spark.storage.blockManagerSlaveTimeoutMs

Before:
WARN  "Removing BlockManager BlockManagerId(201304022120-1976232532-5050-27464-0, myhostname, 51337) with no recent heart beats

After:
WARN  "Removing BlockManager BlockManagerId(201304022120-1976232532-5050-27464-0, myhostname, 51337) with no recent heart beats: 19216ms exceeds 15000ms

Typos: cluser -> cluster

Uniform whitespace across scala examples

Retry failed ssh commands in the ec2 python script.

superstep value upon recomputation, and set the default storage level in
Bagel to MEMORY_AND_DISK

SPARK-724 - Have Akka logging enabled by default for standalone daemons

Conflicts:
	docs/_config.yml
	project/SparkBuild.scala

Conflicts:
	project/SparkBuild.scala

Bumping version for Twitter Algebird to latest

Fixes SPARK-723 - Update build to Scala 2.9.3

Retry failed ssh commands. This is especially useful during system startup when the hosts may not have yet come on-line but can be useful at other points for people with flakey connections

See the JIRA for more details.

I was only able to test the bash version (don't have Windows)
so maybe check over that the syntax is correct there.

corrected Algebird example

Python bugfixes

Fixed broken filter in getWritableClass[T]

Bugfix: WorkerWebUI must respect workDirPath from Worker