User's preferred search tool

[Luca Ferretti <elle uca libero it>]

Hi, 

I've added some patches against libgnome and gnome-control-center on
bugzilla in order to provide, set and use GConf keys to define the
preferred search tool to launch.

The reason is simple: there are several search tools available
(gnome-search-tool, x-nautilus-search:// location, tracker, beagle..)
but GNOME is still hardcoding the use of gnome-search-tool.

You can see this in Places->Search File menu entry and in SEARCH_KEY key
supported by gnome-setting-daemon. 

'cause both are the simplest way to launch a search tool, I think is
really useful make them customizable instead use only gnome-search-tool

The changes are trivial:
      * add new GConf directory /desktop/gnome/applications/search_tool
        with keys exec and needs_terminal  - libgnome, patch ready [1]
      * add new section in Default Applications preferences tool to set
        the preferred tool -
        gnome-control-center/capplets/default-application [2]
      * use the key in gnome-setting-daemon instead hardcoding
        gnome-search-tool (really useful if you have a keyboard with a
        "Search" button on it and you don't use g-s-t as your primary
        tool) - gnome-control-center/gnome-setting-daemon [3]
      * use the key in gnome-panel (as previous, just patch not yet
        ready, sorry) - gnome-panel [4]
      * maybe, but not sure, use in deskbar-applet??

Please comment, review, suggest other presets for default-application
capplet (currently only g-s-t, tracker, beagle and nautilus) and, if you
have to power, allow me to apply on trunk :-)

Cheers, Luca

[1] http://bugs.gnome.org/491647
[2] http://bugs.gnome.org/491650
[3] http://bugs.gnome.org/491652
[4] http://bugs.gnome.org/491654