Add a class to wp_list_bookmarks

[zeo]

Currently there's only a dynamic ID's assigned to each group of bookmarks. For example:

<li id="linkcat-1"><h2>Bookmarks</h2>

It would be great if we assigned a class name to the list.
For example:

<li id="linkcat-1" class="linkcat"><h2>Bookmarks</h2>

This would benefit theme author.

Fixed by [4212]