msql_close() closes the link to a mSQL database that's associated with the specified link identifier. If the link identifier isn't specified, the last opened link is assumed.
如果成功则返回 TRUE，失败则返回 FALSE。
Note that this isn't usually necessary, as non-persistent open links are automatically closed at the end of the script's execution.
msql_close() will not close persistent links generated by msql_pconnect().
See also: msql_connect() and msql_pconnect().