bug#14338: 24.3.50; ELPA package ack fails to install

[chad]

Attempting to install the package `ack', I get:

  Debugger entered--Lisp error: (error "Error during download request: Not 
Found")
    signal(error ("Error during download request: Not Found"))
    error("Error during download request:%s" " Not Found")
    package-handle-response()
    package-download-tar(ack "1.1")
    package-download-transaction((ack))
    package-install(ack)
    mapc(package-install (ack))
    package-menu-execute()
    call-interactively(package-menu-execute nil nil)
    command-execute(package-menu-execute)

This problem has persisted over several days, at least.  To repeat from emacs 
-Q:

        M-x package-list-packages
        <navigate to `ack', version 1.1. It's the first package.>
        i
        x

I verified that other packages can be installed and upgraded, and
that ack can be neither installed nor upgraded (I first noticed it
when trying to upgrade, not with emacs -Q).

~Chad