node_title_list() crashes when you give it a node with a title field

It seems that the node_title_list() function got left behind when node titles were converted to fields in #557292: TF #3: Convert node title to fields.

We now have the odd situation where if you pass a fully-loaded node into this function (i.e., one that came from the Drupal API, via node_load_multiple) then it doesn't work correctly, because it expects $node->title to be a string whereas it's actually an array. It basically only works correctly when it is passed the result of a database query that pulled the node title from {node} directly.

I don't particularly like the fix in the attached patch, but at least it's a start.