Re: Suggested fixes for cperl-mode

First of all this fixes cperl-mode not to set auto-mode-alist (this very incovenient for people who have overridden .pl files to be some other mode), c.f. message on c.e.x from prolog-mode author.

Secondly it makes the default regexp more general. Third, while I was at it it I made cperl-mode use more standard bindings (i.e. not C-h f and C-h v) for its help commands[1]. Moreover I have made the difference C-c C-h f and C-h f to a prefix command for consistency with the rest of Emacs. This latter piece is probably controversial for people whos fingers have the old keybindings rotten in but I think these bindings are a lot cleaner. There may be more than way to do it, but the defaults should be clean.