Return existing selections from addSelection()

Previously if a selection was added and then merged
away the selection-added event would still fire even
though the selection was already destroyed.

Now the existing selection that intersects with the
range is returned when the merge destroys the new selection.

Closes #374

src/app/edit-session.coffee

@@ -584,9 +584,15 @@ class EditSession
     cursor = @addCursor(marker)
     selection = new Selection({editSession: this, marker, cursor})
     @selections.push(selection)
+    selectionBufferRange = selection.getBufferRange()
     @mergeIntersectingSelections()
-    @trigger 'selection-added', selection
-    selection
+    if selection.destroyed
+      for selection in @getSelections()
+        if selection.intersectsBufferRange(selectionBufferRange)
+          return selection
+    else
+      @trigger 'selection-added', selection
+      selection
 
   addSelectionForBufferRange: (bufferRange, options={}) ->
     options = _.defaults({invalidationStrategy: 'never'}, options)