1. Doubleclick a table in ListTables
2. Go back to Database tab and doubleclick another table. -> AV
3. Look at the SQL log - shows at least 2 times the SHOW COLUMNS FROM table
This commit sets the behaviour of PopulateTreeTableList + SetSelectedTable to gracefully ignore the change-events of dbtree while adding or deleting tree items. Avoids unwanted cascaded procedure calls in some places.