Add unsupported state to update manager

src/browser/auto-update-manager.coffee

@@ -7,6 +7,7 @@ CheckingState = 'checking'
 DownladingState = 'downloading'
 UpdateAvailableState = 'update-available'
 NoUpdateAvailableState = 'no-update-available'
+UnsupportedState = 'unsupported'
 ErrorState = 'error'
 
 module.exports =
@@ -53,6 +54,12 @@ class AutoUpdateManager
     unless /\w{7}/.test(@version)
       @check(hidePopups: true)
 
+    switch process.platform
+      when 'win32'
+        @setState(UnsupportedState) unless autoUpdater.supportsUpdates()
+      when 'linux'
+        @setState(UnsupportedState)
+
   emitUpdateAvailableEvent: (windows...) ->
     return unless @releaseVersion? and @releaseNotes
     for atomWindow in windows

src/browser/auto-updater-win32.coffee

@@ -36,6 +36,9 @@ class AutoUpdater
   installUpdate: (callback) ->
     SquirrelUpdate.spawn(['--update', @updateUrl], callback)
 
+  supportsUpdates: ->
+    SquirrelUpdate.existsSync()
+
   checkForUpdates: ->
     throw new Error('Update URL is not set') unless @updateUrl