Fix deletion of VPN gateway route on DHCP renew (bgo #558133)

	* src/NetworkManagerSystem.c
	  src/NetworkManagerSystem.h
		- (nm_system_device_set_ip4_route): return the route that was added
		- (nm_system_add_ip4_vpn_gateway_route): make add_vpn_gateway_route()
			public, clean up, and return the route that was added
		- (nm_system_apply_ip4_config): remove VPN related stuff to simplify,
			since nm_system_add_ip4_vpn_gateway_route() is now available; add
			flags to allow only certain attributes of the NMIP4Config to be
			applied

	* src/nm-device.c
		- (handle_dhcp_lease_change): don't touch the DHCP4 config on failure
		- (nm_device_set_ip4_config): use nm_ip4_config_diff() to only apply
			what's really changed between the old and new configs; don't export
			the new IP4 config on failure; always send the DNS info to the
			named manager

	* src/vpn-manager/nm-vpn-connection.c
		- (device_ip4_config_changed, nm_vpn_connection_new, dispose): track the
			parent device's IP4Config and re-add the VPN gateway route when it
			changes
		- (nm_vpn_connection_ip4_config_get): add the VPN gateway route (since
			nm_system_apply_ip4_config() no longer does) and cache it for later
		- (connection_state_changed): move cleanup code to its own function
		- (vpn_cleanup): delete any previously added VPN gateway route; and
			re-apply the parent device's addresses and routes using
			nm_system_apply_ip4_config(), not nm_device_set_ip4_config()



git-svn-id: http://svn-archive.gnome.org/svn/NetworkManager/trunk@4277 4912f4e0-d625-0410-9fb7-b9a5a253dbdc