Updated Aptana Studio 3 to new version.
Note: Trying to install Pydev using the instructions here: http://download.appcelerator.com/aptana/studio3/pydev/update/stable/ gives the message that 'pydev is already installed'. But Pydev functionality is still not available, and the Preferences menu does not list Pydev.
Reverting to Aptana Studio v3.4.1 restores the Pydev functionality.
Afterward update of Aptana Studio 3, Pydev isn't installed and can't be reinstalled.
Should be seamless, with no steps needed to reinstall Pydev or make sure it isn't clobbered by update.