Merge cursors after buffer changes that didn't occur via the EditSession

The buffer now emits a new event 'update-anchors-after-change' to signal that all the anchors have been updated, which is an appropriate time to merge cursors.

spec/app/edit-session-spec.coffee

@@ -1362,14 +1362,12 @@ describe "EditSession", ->
         [cursor1, cursor2, cursor3] = editSession.getCursors()
         expect(editSession.getCursors().length).toBe 3
 
-        editSession.backspace()
+        buffer.delete([[0, 0], [0, 1]])
+
+        expect(editSession.getCursors().length).toBe 2
         expect(editSession.getCursors()).toEqual [cursor1, cursor3]
         expect(cursor1.getBufferPosition()).toEqual [0,0]
-        expect(cursor3.getBufferPosition()).toEqual [1,0]
-
-        editSession.insertText "x"
-        expect(editSession.lineForBufferRow(0)).toBe "xar quicksort = function () {"
-        expect(editSession.lineForBufferRow(1)).toBe "x var sort = function(items) {"
+        expect(cursor3.getBufferPosition()).toEqual [1,1]
 
   describe "folding", ->
     describe "structural folding", ->

src/app/buffer-change-operation.coffee

@@ -42,6 +42,7 @@ class BufferChangeOperation
     event = { oldRange, newRange, oldText, newText }
     @buffer.trigger 'change', event
     anchor.handleBufferChange(event) for anchor in @buffer.getAnchors()
+    @buffer.trigger 'update-anchors-after-change'
     newRange
 
   calculateNewRange: (oldRange, newText) ->

src/app/edit-session.coffee

@@ -45,7 +45,8 @@ class EditSession
     @buffer.on "path-change.edit-session-#{@id}", =>
       @trigger 'buffer-path-change'
 
-    @buffer.on "change.edit-session-#{@id}", (e) => @mergeCursors()
+    @buffer.on "update-anchors-after-change.edit-session-#{@id}", =>
+      @mergeCursors()
 
     @displayBuffer.on "change.edit-session-#{@id}", (e) =>
       @trigger 'screen-lines-change', e