Corrects a bug in gtk_tree_remove_items and gtk_tree_item_destroy.
Adds the possibility to connect all items by lines. This is the
default now.  You can overide this with the function
gtk_tree_set_view_line which take a tree and a boolean.

This tree widget looks way more finished with the lines.  Very
nice.  Check it out and run gtk/testtree.

-Shawn