Add SparkConf constructor in SharkContext.
Conflicts:
	src/main/scala/shark/SharkEnv.scala
Use lazy SparkConf in KryoSerializer during init.

Guarantees that master and slaves have their own SparkConf references.
Conflicts:
	src/main/scala/shark/execution/serialization/KryoSerializer.scala
Fix NPE in SharkEnv
Slightly refactor SparkConf creation in SharkContext
Merge pull request #265 from harveyfeng/hive11-almost

Refactor SparkConf usage