Fix EXPLAIN plan which was broken in recent change, add test case for EXPLAIN.  Move debug msg in DrillSqlWorker to logger.
AltSort: Replace sort with ExternalSort, Limit + sort with Limit + topN in the generated physical plan.
fix cleanup methods in ExternalSortBatch and TopNBatch.
Bug in ExpressionStringBuilder while parsing timestamp constant.
DRILL-474 - Long.MIN_VALUE is not parsed as BIGINT but as a Double
DRILL-475: TestJdbcQuery fails on Windows due to resource leak
DRILL-476: Create binary_string() function to convert encoded binary string to sequence of bytes
DRILL-477: o.a.d.exec.vector.ValueHolderHelper.getVarCharHolder() creates a BigEndian buffer
DRILL-452: Conversion functions for external data types
DRILL-494: Filter Pushdown into Scan Operator