[1.5.x] Fixed #16992 -- Added InnoDB warning regarding reuse of AUTO_…

…INCREMENT values.

Thanks kent at nsc.liu.se for the report.

Backport of c54fa1a from master

docs/ref/databases.txt

@@ -161,7 +161,10 @@ full-text indexing and searching.
 
 Since MySQL 5.5.5, the default storage engine is InnoDB_. This engine is fully
 transactional and supports foreign key references. It's probably the best
-choice at this point.
+choice at this point. However, note that the the InnoDB autoincrement counter
+is lost on a MySQL restart because it does not remember the
+``AUTO_INCREMENT`` value, instead recreating it as "max(id)+1". This may
+result in an inadvertent reuse of :class:`~django.db.models.AutoField` values.
 
 If you upgrade an existing project to MySQL 5.5.5 and subsequently add some
 tables, ensure that your tables are using the same storage engine (i.e. MyISAM