Use new Configuration() instead of new JobConf() for ObjectWritable.

JobConf's constructor loads default config files in some verisons of
Hadoop, which is quite slow, and we only need the Configuration object
to pass the correct ClassLoader.
Merge pull request #805 from woggle/hadoop-rdd-jobconf

Use new Configuration() instead of slower new JobConf() in SerializableWritable
Report compressed bytes read when calculating TaskMetrics
Merge pull request #808 from pwendell/ui_compressed_bytes

Report compressed bytes read when calculating TaskMetrics
Removing dead docs
Merge pull request #810 from pwendell/dead_doc_code

Remove now dead code inside of docs