Properly exit when render process crashes if exitWhenDone option is true

Previously, we were referring to an undefined `atom` global to exit when
the render process crashed in specs. Now we only exit when exitWhenDone
is true, which will only exit in headless specs. Also, we now call .exit
on an object that's actually defined.

src/browser/atom-application.coffee

@@ -52,6 +52,8 @@ class AtomApplication
   resourcePath: null
   version: null
 
+  exit: (status) -> app.exit(status)
+
   constructor: (options) ->
     {@resourcePath, @version, @devMode} = options
     global.atomApplication = this

src/browser/atom-window.coffee

@@ -18,7 +18,7 @@ class AtomWindow
   isSpec: null
 
   constructor: (settings={}) ->
-    {@resourcePath, pathToOpen, initialLine, @isSpec} = settings
+    {@resourcePath, pathToOpen, initialLine, @isSpec, @exitWhenDone} = settings
     global.atomApplication.addWindow(this)
 
     @setupNodePath(@resourcePath)
@@ -82,7 +82,7 @@ class AtomWindow
       @browserWindow.destroy() if chosen is 0
 
     @browserWindow.on 'crashed', =>
-      atom.exit(100) if @isSpec
+      global.atomApplication.exit(100) if @exitWhenDone
 
       chosen = dialog.showMessageBox @browserWindow,
         type: 'warning'