Do not issue a 'read-only' error in case of DROP TEMPORARY TABLE on a non-existing temporary table.
Instead produce the correct "Unknown table" error or warning (in cases when the IF EXISTS clause was specified).
To a documentor: the part of the manual describing the 'read_only' system variable should be clarified to state the following:
"When the read_only variable is set to ON, all operations which create/update/drop tables are rejected with the exceptions for:
1. Any operation performed by the replication thread on a slave server
2. Any operation performed by a user that have the SUPER privilege
3. Any operation that creates/updates/drops only temporary tables"
the READ_ONLY global variable now allows statements which are to update only temporary tables
(note: if a statement, after parse stage, looks like it will update a non-temp table, it will be rejected,
even if at execution it would have turned out that 0 rows would be updated; for example
UPDATE my_non_tem_table SET a=1 WHERE 1 = 0; will be rejected).
