Catch exceptions thrown by threads launched in ScriptOperator.
Handle SparkHadoopWriter being made non-pubic.

Added a simple CreateJobID() nested function
Synchronize calls to TaskContext#addOnCompleteCallback() in ScriptOperator.
Fix some ScriptOperator spacing
Merge pull request #197 from harveyfeng/script-fix

Catch exceptions thrown by threads launched in ScriptOperator and get Shark to compile with latest Spark master.