Obey the client’s border_width setting (Thanks shatter)

xterm by default sets a border_width of 2. This was not taken into
account when determining the size of the window by i3. Still, you
probably want to set this to 0 in your .Xresources as the pixels
are just lost.

include/data.h

@@ -352,6 +352,9 @@ struct Client {
         int base_height;
         int base_width;
 
+        /** The amount of pixels which X will draw around the client. */
+        int border_width;
+
         /** contains the minimum increment size as specified for the window
          * (in pixels). */
         int width_increment;

include/manage.h

@@ -42,6 +42,7 @@ void manage_window(xcb_property_handlers_t *prophs, xcb_connection_t *conn,
  */
 void reparent_window(xcb_connection_t *conn, xcb_window_t child,
                      xcb_visualid_t visual, xcb_window_t root, uint8_t depth,
-                     int16_t x, int16_t y, uint16_t width, uint16_t height);
+                     int16_t x, int16_t y, uint16_t width, uint16_t height,
+                     uint32_t border_width);
 
 #endif