devdraw: fix retina mode

R=rsc
http://codereview.appspot.com/6847104
diff --git a/src/cmd/devdraw/cocoa-screen.m b/src/cmd/devdraw/cocoa-screen.m
index 24baca1..a2ff3d4 100644
--- a/src/cmd/devdraw/cocoa-screen.m
+++ b/src/cmd/devdraw/cocoa-screen.m
@@ -1408,7 +1408,7 @@
 static NSSize
 winsizepixels()
 {
-#if DOSX_VERSION >= 100700
+#if OSX_VERSION >= 100700
 	if (OSX_VERSION >= 100700 && devdrawretina)
 		return [win.content convertSizeToBacking: winsizepoints()];
 	else