PRIVILEGE.

Backport from mysql-5.7 to mysql-5.5 and mysql-5.6.

BUG#13969578: TEMPORARY TABLE IN A DATABASE ON A READ-ONLY
                  INSTANCE CAN BE OVERWRITTEN

Analysis:
========

Creation or modification of a persistent table by a non-super user
is NOT ALLOWED in read_only mode. Only TEMPORARY tables are allowed
to be created or modified in read_only mode. But the creation of
a persistent table was being allowed when a temporary table of
the same name existed.

The routine which denies updating a non-temporary table in a
read_only mode does not handle the case of creation of a regular
table when a temporary table of the same exists.

Fix:
===
Handled the condition where an attempt is made to create a persistent
table having the same name as that of the temporary table. Hence
the creation of a persistent table by a non-super user when a
temporary table of the same exists is denied under read_only mode.