When using the 'make update' command, allow the application to be optionally specified on the command line.  For example:
When using the 'make update' command, allow the application to be optionally specified on the command line.  For example:

   make update APPID=chromiumcodereviews-hr VERSION=r123-4567890abc

If APPID is specified, then the application from the app.yaml file is used.

Review: http://codereview.appspot.com/6138054/

riannucci/rietveldv2,riannucci/rietveldv2