Merge pull request #12 from jhartlaub/shark-0.9-amplab

Apply backport of HIVE-4122 - NULL timestamp handling bug fix.
Explicitly set javac's source and target versions
Merge pull request #14 from jey/explicitly-specify-javac-versions

Explicitly set javac's source and target versions
fix synchronization issue, which used frequently in Text comparison
fix the indirect synchronized issue in multi-thread env for constant & determined expr evaluation
Merge pull request #15 from chenghao-intel/synchronized_fixes

Two fixes that reduce contention in multithreaded environment for expression evaluations.
Fix concurrency issue with SimpleDateFormat (not thread-safe), make dateFormat ThreadLocal<DateFormat> to
avoid Timestamp data corruption (manifesting during CTAS and operations).