added default spacing

lib/compass/sass_extensions/functions/sprites.rb

@@ -4,11 +4,12 @@ module Compass::SassExtensions::Functions::Sprites
     path, name = Compass::Sprites.path_and_name(uri)
     y = 0
     last_spacing = 0
+    default_spacing = number_from_var("#{name}-spacing")
     images = Compass::Sprites.sprites(name)
     images.each do |image|
       current_spacing = number_from_var("#{name}-#{image[:name]}-spacing")
       if y > 0
-        y += current_spacing > last_spacing ? current_spacing : last_spacing
+        y += [current_spacing, last_spacing, default_spacing].max
       end
       image[:y] = y
       y += image[:height]

spec/sprites_spec.rb

@@ -196,5 +196,26 @@ describe Compass::Sprites do
       }
     CSS
   end
+
+  it "should calculate the default spacing between images" do
+    css = render <<-SCSS
+      $squares-spacing: 22px;
+      @import "squares/*.png";
+      @include all-squares-sprites;
+    SCSS
+    css.should == <<-CSS
+      .squares-sprite, .squares-10x10, .squares-20x20 {
+        background: url('/squares.png') no-repeat;
+      }
+      
+      .squares-10x10 {
+        background-position: 0 0;
+      }
+      
+      .squares-20x20 {
+        background-position: 0 -32px;
+      }
+    CSS
+  end
   
 end