Merge Hadoop Into Spark

This patch merges the Hadoop 0.20.2 source code into the Spark project. I've thought about this a bunch and this will provide us with several benefits:

### More source code
Let's be honest, to be taken seriously as a project Spark needs to have _way more_ lines of code. Spark is currently 70,000 lines of Scala code - this patch adds 452,000 lines of XML alone (!) This will make our github stats look great!

### Seamless builds
Sometimes users stumble trying to build Spark against Hadoop. Not anymore!! With Hadoop inside of Spark this won't a problem at all. I mean, there's basically only one Hadoop version, right? So this should work for pretty much everyone. Wait, hold on, is hadoop-0.20.2 the same as hadoop-2.2.0? I'm assuming it's the same because they both have the same number of "2"s.

### Your favorite old configs
This patch will give users access to some of their favorite old configs from Hadoop. Did you just figure out what `dfs.namenode.path.based.cache.block.map.allocation.percent` was?! Now you can use it in Spark!! Pining for your old friend `mapreduce.map.skip.proc.count.autoincr`... fuggedabodit - we got ya!

I plan to contribute tests and docs in a subsequent patch. Please merge this ASAP and include in Spark 0.9.1.

**NB: This diff is too large for github to render. Users will have to download and play with this on their own.**