Account for queries handled by query-cache in USER_STATISTICS (and in HOST_STATISTICS)

[Affected version: at least 5.5.28a-MariaDB-log]

When a user performs queries handled by query-cache theses are not taken into account by USER_STATISTICS (and probably neither by HOST_STATISTICS).

They should properly increment COMMAND_SELECT, SENT_ROWS and when appropriate EMPTY_QUERIES.

Without updating those a user that performs the same SELECT over and over, each time hitting query cache will appear as performing no queries, just burning CPU time and exchanging bytes.