Fix TypeError on drop_column for SQLite

It uses now tuple unpacking on the loop.
It was introduced in changeset a3ef75ef8f6a

issue2647
review32641002

trytond/backend/sqlite/table.py

@@ -299,10 +299,10 @@ class TableHandler(TableHandlerInterface):
             logger.warning('Unable to drop column: Error renaming '
                 'table %s to temp!', self.table_name)
         new_table = TableHandler(self._model, history=self.history)
-        for col in self._columns.iteritems():
-            if col != column_name:
-                new_table.add_raw_column(col, col['typname'], True,
-                    field_size=col['size'])
+        for name, column in self._columns.iteritems():
+            if name != column_name:
+                new_table.add_raw_column(name, column['typname'], True,
+                    field_size=column['size'])
         columns_name = [x for x in new_table._columns.keys()]
         cursor.execute(('INSERT INTO "%s" (' +
                         ','.join('"%s"' % c for c in columns_name) +