Log Message:
Declare that misc/elscreen does not support Emacs 24 or later

It uses some of obsolete variables/functions, resulting in an error on
Emacs 24 or later like this:

  string-to-number: Symbol's value as variable is void: last-command-char

I have recently created wip/elscreen-current for this
reason. Unfortunately it doesn't have a version number nor a release
tarball since it's an unofficial fork of the original ElScreen, even
though it's what MELPA currently provides: http://melpa.org/#/elscreen