Fix bug in SparkLoadTask for `CACHE <partitioned_table>`

Each partition would result in a new partitioned table entry ...
Allow users to control the number of tasks for table scan operations
This will enable user's queries to perform well even for high cardinality partitioned tables
Merge pull request #305 from sundeepn/coalesce

Allow users to control the number of tasks for table scan operations
Merge pull request #296 from harveyfeng/master

Fix bug in SparkLoadTask for `CACHE <partitioned_table>`
CG (Row/OI) & Example for SelectOperator
integrated expr cg with shark
fix couple of small bugs of corner cases
fix bugs of condition branch
update the repo for accessiable from CN
fix bunch of small bugs
fix bug of equals for TENUDF/TENGUDF
fix bug in CSE
optimize the EENGuardNull
Replace the EENAttribute with EENInputRow in leaf node
fix NPE in cse EENInputRow
Using the OI for input instead of the CGRow, to avoid the unneccessary field deserialization
Constant Folding Support
fix bug of result type integer for short+short
fix bug in conditional branch
remove the null check for constant value