Support 'require_relative' in rubies less than v1.9.2

lib/require_relative.rb

@@ -0,0 +1,21 @@
+# require_relative was introduced in 1.9.2. This makes it
+# available to younger rubies.  It trys hard to not re-require
+# files.
+
+unless Kernel.respond_to?( :require_relative )
+  module Kernel
+    def require_relative( path )
+      desired_path = File.expand_path( '../' + path.to_str, caller[0] )
+      shortest = desired_path
+      $:.each do |path|
+        path += '/'
+        if desired_path.index( path ) == 0
+          candidate = desired_path.sub( path, '' )
+          shortest = candidate if candidate.size < shortest.size
+        end
+      end
+      require shortest
+    end
+  end
+end
+