bug#3746: M-r in comint mode should use isearch

[Dan Nicolaescu <dann@ics.uci.edu>]

Juri Linkov <juri@jurta.org> writes:

  > > When using the minibuffer for example doing:
  > >
  > > M-x
  > > then
  > > C-r
  > > will use isearch to search the history.  This is nice because it shows
  > > the items that are matched.
  > >
  > > M-r should to the same thing when used in comint, right now it's hard
  > > to tell if it matches anything before typing RET
  > 
  > Do you mean implementing a bash-like history isearch
  > in comint/shell modes?  I think it would be nice.

Yep.

  > But maybe M-r is not the best key to start a shell history
  > isearch in the comint buffer.  In the minibuffer M-r keeps
  > its old functionality, and C-s is used to isearch the
  > minibuffer history.

The problem with that is that C-s (and C-r) already have bindings in
comint modes, and changing them would not be liked by most users.
Doing M-r and then C-s/C-r seems a bit cumbersome. 
IMHO just using M-r for incremental history search will provide no
surprises for the user, and it seems like a natural extension of the
current behavior.