bug#14742: 24.3.50; enhancement request: be able to prepend stuff from buffer when search backward

[Juri Linkov <juri@jurta.org>]

>> and since then I have not had problems with it.  So what could
>> be done is to move this code from `isearch-other-meta-char'
>> to `isearch-yank-string' and `isearch-del-char' for more
>> general functionality by adding a new argument `BACK' to them
>> (or could you propose a better name for the argument).
>
> I take your word for it wrt the implementation.  After I see it,
> I might have a suggestion wrt the name (maybe BACKWARD, as that
> seems to be the term used in our search names).

It's easy to find a name for the new arg of `isearch-yank-string'.
By default, it appends a string to the end of the search string,
so a new arg for opposite meaning could have the name `prepend'
to prepend a string to the beginning of the search string.

But what could be a name for the new arg of `isearch-del-char'?
By default, it deletes a substring from the end of the search string.
And with a non-nil new arg it will delete a substring from the
beginning of the search string.  What about the name `behead'
suggested in
http://english.stackexchange.com/questions/111382/what-are-the-antonyms-of-append-and-prepend

=== modified file 'lisp/isearch.el'
--- lisp/isearch.el	2013-06-13 22:08:45 +0000
+++ lisp/isearch.el	2013-06-29 21:50:03 +0000
@@ -1839,7 +1839,7 @@ (defun isearch-delete-char ()
     (isearch-pop-state))
   (isearch-update))
 
-(defun isearch-del-char (&optional arg)
+(defun isearch-del-char (&optional arg behead)
   "Delete character from end of search string and search again.
 Unlike `isearch-delete-char', it only deletes the last character,
 but doesn't cancel the effect of other isearch command.
@@ -1847,9 +1847,13 @@ (defun isearch-del-char (&optional arg)
   (interactive "p")
   (if (= 0 (length isearch-string))
       (ding)
-    (setq isearch-string (substring isearch-string 0
-				    (- (min (or arg 1)
-					    (length isearch-string))))
+    (setq isearch-string (if behead
+			     (substring isearch-string
+					(min (or arg 1)
+					     (length isearch-string)))
+			   (substring isearch-string 0
+				      (- (min (or arg 1)
+					      (length isearch-string)))))
           isearch-message (mapconcat 'isearch-text-char-description
                                      isearch-string "")))
   ;; Use the isearch-other-end as new starting point to be able
@@ -1858,17 +1862,23 @@ (defun isearch-del-char (&optional arg)
    (isearch-push-state)
    (isearch-update)))
 
-(defun isearch-yank-string (string)
+(defun isearch-yank-string (string &optional prepend)
   "Pull STRING into search string."
   ;; Downcase the string if not supposed to case-fold yanked strings.
   (if (and isearch-case-fold-search
 	   (eq 'not-yanks search-upper-case))
       (setq string (downcase string)))
   (if isearch-regexp (setq string (regexp-quote string)))
-  (setq isearch-string (concat isearch-string string)
+  (setq isearch-string (if prepend
+			   (concat string isearch-string)
+			 (concat isearch-string string))
 	isearch-message
 	(concat isearch-message
 		(mapconcat 'isearch-text-char-description