improve pg sql parser

src/main/java/com/alibaba/druid/sql/ast/expr/SQLBinaryOperator.java

@@ -68,9 +68,7 @@ public enum SQLBinaryOperator {
     BooleanAnd("AND", 140), 
     BooleanXor("XOR", 150), 
     BooleanOr("OR", 160), 
-    Assignment(":=", 169),
-    
-    PostgresStyleTypeCast("::", 20),
+    Assignment(":=", 169)    
     ;
 
     public static int getPriority(SQLBinaryOperator operator) {

src/main/java/com/alibaba/druid/sql/ast/expr/SQLCastExpr.java

@@ -22,8 +22,8 @@ import com.alibaba.druid.sql.visitor.SQLASTVisitor;
 
 public class SQLCastExpr extends SQLExprImpl {
 
-    private SQLExpr     expr;
-    private SQLDataType dataType;
+    protected SQLExpr     expr;
+    protected SQLDataType dataType;
 
     public SQLCastExpr(){