#32 [PHP]Simplify the code of cubrid_client_encoding and cubrid_get_charset

[Jira Trac]

[cubrid_client_encoding|http://www.php.net/manual/en/function.cubrid-client-encoding.php] is supported for MySQL compatibility. But the implement of this function is similar to [cubrid_get_charset|http://www.php.net/manual/en/function.cubrid-get-charset.php]. So we need to simplify the source code and pick up the same code segment.