bug#14695: 24.3.50; perl-mode: Provide user option selecting indentation style

[Jambunathan K]

Perl-mode says there are different styles of indentation.  See below.
Unfortunately, I couldn't find a single place to select a particular
style.  (Think `c-set-style' and `c-style-alist').

,----
| Various indentation styles:       K&R  BSD  BLK  GNU  LW
|   perl-indent-level                5    8    0    2    4
|   perl-continued-statement-offset  5    8    4    2    4
|   perl-continued-brace-offset      0    0    0    0   -4
|   perl-brace-offset               -5   -8    0    0    0
|   perl-brace-imaginary-offset      0    0    4    0    0
|   perl-label-offset               -5   -8   -2   -2   -2
`----

Side note: I am porting Oddmuse to support Org-mode style markup.  The
default values of the above variables chosen by `perl-mode' (LW style)
and that used in Oddmuse itself (GNU style) seems to be different.

So please review the default choice of style once named styles are
introduced.  Should it be LW or GNU...

In GNU Emacs 24.3.50.1 (i686-pc-linux-gnu, GTK+ Version 2.20.1)
 of 2013-06-22 on debian-6.05
Bzr revision: 113135 lekktu@gmail.com-20130622024114-o1weajdmsssio1vk
Windowing system distributor `The X.Org Foundation', version 11.0.10707000
Important settings:
  value of $LANG: en_IN
  locale-coding-system: iso-latin-1-unix
  default enable-multibyte-characters: t