Changed tabs to spaces.

sed -i 's/	/    /g' files
cache demo - fixed mysql connection closing.

 - added thread_init() and thread_end() to db_cache destructor,
   since it belongs to main thread.
 - added check in mysql_client's destructor.
 - in mysql_client::get_connection delete connection pointer if connection
   is closed, then create a new connection.
 - added commentary in mysql_client.
cache demo - mysql_client removed exception handling.
cache demo - db_client: removed shared_ptr.