Minor style cleanup. Mostly on indenting & line width changes.
Fixing config option "retained_stages" => "retainedStages".

This is a very esoteric option and it's out of sync with the style we use.
So it seems fitting to fix it for 0.9.0.
Merge pull request #364 from pwendell/fix

Fixing config option "retained_stages" => "retainedStages".

This is a very esoteric option and it's out of sync with the style we use.
So it seems fitting to fix it for 0.9.0.
Don't delegate to users `sbt`.

This changes our `sbt/sbt` script to not delegate to the user's `sbt`
even if it is present. If users already have sbt installed and they
want to use their own sbt, we'd expect them to just call sbt directly
from within Spark. We no longer set any enironment variables or anything
from this script, so they should just launch sbt directly on their own.

There are a number of hard-to-debug issues which can come from the
current appraoch. One is if the user is unaware of an existing sbt
installation and now without explanation their build breaks because
they haven't configured options correctly (such as permgen size)
within their sbt. Another is if the user has a much older version
of sbt hanging around, in which case some of the older versions
don't acutally work well when newer verisons of sbt are specified
in the build file (reported by @marmbrus). A third is if the user
has done some other modification to their sbt script, such as
setting it to delegate to sbt/sbt in Spark, and this causes
that to break (also reported by @marmbrus).

So to keep things simple let's just avoid this path and
remove it. Any user who already has sbt and wants to build
spark with it should be able to understand easily how to do it.
Small typo fix
Minor update on SparkContext.broadcast's JavaDoc.
Merge pull request #368 from pwendell/sbt-fix

Don't delegate to users `sbt`.

This changes our `sbt/sbt` script to not delegate to the user's `sbt`
even if it is present. If users already have sbt installed and they
want to use their own sbt, we'd expect them to just call sbt directly
from within Spark. We no longer set any enironment variables or anything
from this script, so they should just launch sbt directly on their own.

There are a number of hard-to-debug issues which can come from the
current appraoch. One is if the user is unaware of an existing sbt
installation and now without explanation their build breaks because
they haven't configured options correctly (such as permgen size)
within their sbt (reported by @patmcdonough). Another is if the user has a much older version
of sbt hanging around, in which case some of the older versions
don't acutally work well when newer verisons of sbt are specified
in the build file (reported by @marmbrus). A third is if the user
has done some other modification to their sbt script, such as
setting it to delegate to sbt/sbt in Spark, and this causes
that to break (also reported by @marmbrus).

So to keep things simple let's just avoid this path and
remove it. Any user who already has sbt and wants to build
spark with it should be able to understand easily how to do it.
Merge pull request #361 from rxin/clean

Minor style cleanup. Mostly on indenting & line width changes.

Focused on the few important files since they are the files that new contributors usually read first.