ensure relative_require on root of uri:classloader:/

this fixes a regression of 0137667

Sponsored by Lookout Inc.

Author: mkristian

core/src/main/java/org/jruby/util/URLResource.java

@@ -163,7 +163,7 @@ public static FileResource createClassloaderURI(Ruby runtime, String pathname) {
         }
         URL url = cl.getResource(pathname);
         String[] files = listClassLoaderFiles(cl, pathname);
-        return new URLResource(URI_CLASSLOADER + pathname,
+        return new URLResource(URI_CLASSLOADER + "/" + pathname,
                                cl,
                                url == null ? null : pathname,
                                files);

test/relative.rb

@@ -0,0 +1 @@
+require_relative 'relative'

test/require_relative.rb

@@ -46,6 +46,14 @@ def test_require
     assert $loaded_foo_bar
   end
 
+  # GH-2972
+  def test_require_relative_via_uri_classloader_protocol
+    $CLASSPATH << './test'
+    assert_nothing_raised do
+      require 'uri:classloader:/require_relative.rb'
+    end
+  end
+
   # JRUBY-3231
   def test_load_with_empty_string_in_loadpath
     begin