search-provider: Use AM_CPPFLAGS rather than INCLUDES

This is deprecated in newer automake versions, and this causes warnings
with automake 1.14:
panels/printers/Makefile.am:3: warning: 'INCLUDES' is the old name for
AM_CPPFLAGS' (or '*_CPPFLAGS')

https://bugzilla.gnome.org/show_bug.cgi?id=732189

search-provider/Makefile.am

@@ -12,7 +12,8 @@ $(dbus_shell_search_provider_built_sources) : Makefile.am $(srcdir)/org.gnome.Sh
 		$(srcdir)/org.gnome.ShellSearchProvider2.xml		\
 		$(NULL)
 
-INCLUDES =					\
+AM_CPPFLAGS =					\
+	-DGNOMELOCALEDIR="\"$(datadir)/locale\""\
 	-DCC_PANEL_LOADER_NO_GTYPES		\
 	-I$(top_srcdir)				\
 	$(SHELL_CFLAGS)				\
@@ -37,8 +38,6 @@ gnome_control_center_search_provider_LDADD =	\
 	$(top_builddir)/shell/libshell.la	\
 	$(SHELL_LIBS)
 
-AM_CPPFLAGS = -DGNOMELOCALEDIR="\"$(datadir)/locale\""
-
 CLEANFILES = $(BUILT_SOURCES) $(service_DATA)
 
 servicedir = $(datadir)/dbus-1/services