+'ApiFeedContributions::feedItem': Called to convert the result of ContribsPager
+into a FeedItem instance that ApiFeedContributions can consume. Implementors of
+this hook may cancel the hook to signal that the item is not viewable in the
+provided context.
+$row: A row of data from ContribsPager. The set of data returned by ContribsPager
+ can be adjusted by handling the ContribsPager::reallyDoQuery hook.
+$context: An IContextSource implementation.
+&$feedItem: Set this to a FeedItem instance if the callback can handle the provided
+ row. This is provided to the hook as a null, if it is non null then another callback
+ has already handled the hook.
+