This patch keeps emacs from printing the history messages when performing a history search in a comint buffer.  (For example, M-x shell RET M-r o).

Changelog:

2013-04-28  Tim Daly Jr.  <tim@tenkan.org>

	* comint.el (comint-history-isearch-in-progress): new variable
	that lets us detect that an isearch is running over command
	history
	(comint-previous-matching-input): don't print "History item: N"
	messages when called as part of an isearch over history, because
	it's too slow and spammy.
	(comint-history-isearch-setup, comint-history-isearch-end): toggle
	comint-history-isearch-in-progress to indicate search start and
	stop

Patch: