invoke cper-mode instead of perl-mode

[Harry Putnam]

There must be more to do than add to auto-mode-alist, to get emacs to
open perl scripts in cperl mode.

I have this in .emacs:
(wrapped for mail)
 (setq auto-mode-alist
     (cons '("\\.\\([pP]\\([Llm]\\|erl\\)\\|al\\)\\'" . cperl-mode )
          auto-mode-alist))

Which does work on any files matching the regex, but still, files
with no extension but are still perl scripts with the perl shebang
get opened in perl-mode instead of cperl-mode.  I don't see this
explained under `How Major Modes are Chosen' or `Major Modes' in the
manual so apparently it is another variable that does this.

A further problem is that files that emacs knows how to open get
opened with abbrev-mode enabled.  But the ones openned in cperl-mode
do not have abbrev-mode enabled.

I have these in .emacs:
(setq default-abbrev-mode t)
(read-abbrev-file)