Grid image generation: Fix a double output issue, let write_file handle dry runs, and make sure to open the file for binary output.

lib/compass/grid_builder.rb

@@ -93,12 +93,7 @@ module Compass
         end
       end
       directory File.dirname(filename)
-      logger.record((overwrite ? :overwrite : :create), basename(filename))
+      write_file(filename, self.to_blob, options, true)
-      unless options[:dry_run]    
-        write_file(filename, self.to_blob)
-      else
-        true
-      end
     end
   end
 end