prepare all subqueries object before launch subqueries. and add some check for global status object  during super table query.

add the union support in sql parser: fix memory leaks and refactor some functions, improve the performance of some functions. #1032. [TBASE-1140]

fix the invalid release operations when the database is dropped and the metermeta cache is cleaned up at the client side. #1053  [tbase-1435]

add the union support in sql parser. refactor some codes. fix bug in join query caused by feature update #1032. [TBASE-1140]

add the null-terminated char for the binary data, if the space if available.