Allow configure image path for boxed-bg.jpg

build/less/core.less

@@ -35,7 +35,7 @@ body {
 }
 
 .layout-boxed {
-  background: url('../img/boxed-bg.jpg') repeat fixed;
+  background: url('@{image-path}/boxed-bg.jpg') repeat fixed;
 }
 
 /*

build/less/variables.less

@@ -1,6 +1,11 @@
 //AdminLTE 2 Variables.less
 //=========================
 
+//PATHS
+//--------------------------------------------------------
+
+@image-path: "../img";
+
 //COLORS
 //--------------------------------------------------------