moodle_read_slave_trait: when creating another handle, restore temptables
property that is clobbered by raw_connect().
Also a better condition for temptable related queries detection in
pgsql_native_moodle_database.
dml_pgsql_read_slave_test::test_temp_table(): use real db connection
if possible, otherwise skip the test.
Implemented with moodle_read_slave_trait
Functionality is triggered by supplying config dboption['readonly'].
See config-dist.php for more info on supported dboptions.
pgsql and mysqli drivers are using this feature. Also added support for
connection timeout for these two drivers.
Srdjan