[PATCH] Doctrine_Collection::isModified() does not support deep like Doctrine_Record but probably should

$record instanceof Doctrine_Record;
$collection instanceof Doctrine_Collection;

Using the $record object I can find out if it has been modified : $record->isModified().
I can also have this check all the relations also by passing true : $record->isModified(true);

However, the $collection object only support the first level and not the relations of its member records,
$collection->isModified() returns false if one of the entry has one its relations modified (as it should).

The improvement would be to allow this method to accept true, like it's $record counterpart, which would return true instead.

See attached patch.