Drop-in replacement for vanilla perl-mode.el for Emacs 24.

This file was copied verbatim from the perl-mode.el packaged with my
version of Emacs (24.3 packaged for Ubuntu 13.10).  It is meant to be
loaded instead of the regular perl-mode.el.
Merge pull request #156 from fgabolde/master

Drop-in replacement for vanilla perl-mode.el for Emacs 24.