bug#12638: 24.2.50; FR: Some suggestions for icomplete-mode

[Jambunathan K <kjambunathan@gmail.com>]

I have turned on icomplete mode following a suggestion in this message
http://debbugs.gnu.org/cgi/bugreport.cgi?bug=11131#20.

Since I do use ido-mode, I am wondering whether the icomplete UI could
be modified to match ido UI.  This is to ensure uniformity of
experience.

A cursory look at ido.el suggests that it is indeed derived from
icomplete.el but has been specialized for handling files and buffers.
So there is much common ground between the two modes.

Some observations and initial thoughts:

1. The icomplete candidates are comma separated but WITHOUT spaces.  It
   makes readability difficult.
   
   So introduce `icomplete-decorations' which can be a copy of
   `ido-decorations' to begin with.  May be the decorations could be
   extracted to some other file (minibuffer.el?) and commonly shared by
   both ido and icomplete.

2. Support for cycling via C-s and C-r, highlighting and selection of
   current head (all much like ido-mode)

3. (May be) substring matching.  (Is there a way to accomplish this
   already, I am not sure.)

I can prepare a patch for (1).

Other items have to wait till my foo in related areas improves.

In GNU Emacs 24.2.50.19 (i686-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2012-10-13 on debian-6.05
Bzr revision: 110533 cyd@gnu.org-20121013095159-t6cou0e9o2g2vg8g
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