bug#15513: 24.2; isearch should clear selection in transient-mark-mode

[Stefan Monnier <monnier@iro.umontreal.ca>]

retitle 15513 Isearch should clear shift-selected region
thanks

> 3. Select the word This by pressing Ctrl+Shift+Right arrow.
> 4. Invoke isearch by pressing Ctrl+S.
[...]
> Observed behavior:
> * Selection is extended to include the word that was found by isearch.
> Expected behavior:
> * Since isearch is a point movement command and such commands deactivate
> the selection in transient-mark-mode, I expect selection to be
> deactivated.
> * If I press Ctrl+Space before searching, this indicates an explicit
> request for persistent selection.  In this case, the current behavior of
> isearch is correct.

Actually, any highlighted region is a transient region.  Motion commands
deactivate the current selection only in the case where the selection
was made with shifted motion commands.

So C-s should only deactivate the region if it has been activated by
shifted motion commands.

> * Additionally, it might be nice if pressing Ctrl+Shift+S behaved
> similarly to Shift+arrow keys, unconditionally activating the selection
> and extending/shrinking it to include the match.

Yes, that would make a lot of sense, although C-S-s in my setup seems
never to reach Emacs (probably caught by something like
a window-manager).


        Stefan