Fix drag_info in citationtreeview, so that it doesn't break merge citation. Also add some comments about drag and drop.

svn: r18443

src/ScratchPad.py

@@ -142,6 +142,15 @@ def obj2target(target):
          }
     return d[target] if target in d else None
 
+# FIXME: CITATION: Dropping a citation onto an embedded tab should open 
+# CitationEdit. However, note should behave similarly, and although there is
+# code to call EditNote, EditNote does not appear to be called. I don't
+# understand how to get the editor called.
+
+# FIXME: CITATION: It should be possible to drop a source onto an embedded tab,
+# with CitationEdit being opened, However, It is not possible to do the drop,
+# and as described above I do not understand how to get the editor called.
+
 def model_contains(model, data):
     """
     Returns True if data is a row in model.