Eng 6390 jdbc resultset

Wrote the test cases (as per issue description) for HSQL JDBCResultSet and VoltDB JDBC4ResultSet (for Empty and Non-Empty tables) and compared the corresponding results.

Fixed the cursor navigations in the scrollable JDBC4ResultSet for forward and backward navigations and all the boundary cases.
Also, since the cursor can't simultaneously be After Last and Before First, I would use an enum rather than 2 booleans. That way you only have to update the enum when you move to a valid row rather than updating both bools all over the place.