Don't prompt to save if buffer is opened elsewhere

This corrects a regression where closing an edit session that
is opened somewhere else should not prompt to save since it
won't be lost if closed immediately since it is still open in
another pane.

spec/app/edit-session-spec.coffee

@@ -2358,3 +2358,13 @@ describe "EditSession", ->
           editSession.joinLine()
           expect(editSession.lineForBufferRow(9)).toBe '  }; return sort(Array.apply(this, arguments)); };'
           expect(editSession.getSelectedBufferRange()).toEqual [[9, 3], [9, 49]]
+
+  describe ".shouldPromptToSave()", ->
+    it "returns false when an edit session's buffer is in use by more than one session", ->
+      expect(editSession.shouldPromptToSave()).toBeFalsy()
+      buffer.setText('changed')
+      expect(editSession.shouldPromptToSave()).toBeTruthy()
+      editSession2 = project.buildEditSession('sample.js', autoIndent: false)
+      expect(editSession.shouldPromptToSave()).toBeFalsy()
+      editSession2.destroy()
+      expect(editSession.shouldPromptToSave()).toBeTruthy()

src/app/edit-session.coffee

@@ -168,7 +168,7 @@ class EditSession
   scanInBufferRange: (args...) -> @buffer.scanInRange(args...)
   backwardsScanInBufferRange: (args...) -> @buffer.backwardsScanInRange(args...)
   isModified: -> @buffer.isModified()
-  hasEditors: -> @buffer.hasEditors()
+  shouldPromptToSave: -> @isModified() and not @buffer.hasMultipleEditors()
 
   screenPositionForBufferPosition: (bufferPosition, options) -> @displayBuffer.screenPositionForBufferPosition(bufferPosition, options)
   bufferPositionForScreenPosition: (screenPosition, options) -> @displayBuffer.bufferPositionForScreenPosition(screenPosition, options)

src/app/pane.coffee

@@ -148,7 +148,7 @@ class Pane extends View
 
     @autosaveItem(item)
 
-    if item.isModified?()
+    if item.shouldPromptToSave?()
       @promptToSaveItem(item, reallyDestroyItem)
     else
       reallyDestroyItem()

src/app/text-buffer.coffee

@@ -70,7 +70,7 @@ class Buffer
     path: @getPath()
     text: @getText() if @isModified()
 
-  hasEditors: -> @refcount > 1
+  hasMultipleEditors: -> @refcount > 1
 
   subscribeToFile: ->
     @file.on "contents-changed", =>