rxvt hardwired for X11R6, so ensure dependency is OK

package/rxvt/Config.in

@@ -1,7 +1,10 @@
 config BR2_PACKAGE_RXVT
 	bool "rxvt"
 	default n
+	depends BR2_PACKAGE_XSERVER_xorg || BR2_PACKAGE_XSERVER_tinyx
+
 	help
 	  A nice small colour vt102 X terminal emulator.
+	  Does not build for X11R7 yet.
 
 	  http://www.rxvt.org/