Rename frame_create and frame_set_child_size with a window_ prefix

This is to avoid a collision with an actual frame structure.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
diff --git a/clients/image.c b/clients/image.c
index 4d3f3b8..c73d0c0 100644
--- a/clients/image.c
+++ b/clients/image.c
@@ -378,7 +378,7 @@
 	}
 
 	image->window = window_create(display);
-	image->widget = frame_create(image->window, image);
+	image->widget = window_frame_create(image->window, image);
 	window_set_title(image->window, title);
 	image->display = display;
 	image->image_counter = image_counter;