search/browse button

	* src/nautilus-location-bar.h, src/nautilus-location-bar.c:
	Factored this into two classes, NautilusNavigationBar, a class
	that defines the abstract interface (the set_location function and
	the location_changed signal), and NautilusLocationBar, a concrete
	implementation that works like the previous location bar.
	(nautilus_location_bar_set_location,
	nautilus_location_bar_get_location): Made static. Made
	`nautilus_location_bar_set_location' the handler for the
	set_location virtual method.
	* src/nautilus-navigation-bar.h, src/nautilus-navigation-bar.c:
	Abstract superclass for navigation bars.
	* src/nautilus-search-bar.h, src/nautilus-search-bar.c: New
	subclass of NautilusNavigationBar. Contains placeholder widgets
	for now, will eventually be the search bar.
	* src/nautilus-switchable-navigation-bar.h,
	src/nautilus-switchable-navigation-bar.c: New subclass of
	NautilusNavigationBar that allows switching between the location
	bar and the search bar.
	* src/nautilus-window.h: Rename `ent_uri' member of the window
	struct to `navigation_bar'.
	* src/nautilus-window.c
	(nautilus_window_navigation_bar_mode_changed_callback): Callback
	to sync the "search" toggle button to the mode of the switchable
	navigation bar.
	(nautilus_window_constructed): Create a
	NautilusSwitchableNavigationBar instead of a NautilusLocationBar.
	(nautilus_window_set_search_mode): New function to be used by the
	search toggle button callback; simply sets the mode of the
	switchable navigation bar appropriately.
	* src/nautilus-window-toolbars.c: Made Search button a toggle
	button.
	(toolbar_search_callback): Call `nautilus_window_set_search_mode'.
	* src/nautilus-window-manage-views.c
	(nautilus_window_update_internals,
	nautilus_window_end_location_change_callback): Use
	NautlusNavigationBar calls instead of NautilusLocationBar ones.
	* src/Makefile.am: Add new files to the build, and split all
	headers into noinst_HEADERS out from the nautilus_SOURCES
	variable.