Revert r42938 "* lib/rubygems: Update to RubyGems 2.1.3"

It breaks build.
http://u64.rubyci.org/~chkbuild/ruby-trunk/log/20130913T200302Z.diff.html.gz

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42941 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rubygems/core_ext/kernel_require.rb

@@ -48,7 +48,12 @@ module Kernel
     # normal require handle loading a gem from the rescue below.
 
     if Gem::Specification.unresolved_deps.empty? then
-      return gem_original_require(path)
+      begin
+        RUBYGEMS_ACTIVATION_MONITOR.exit
+        return gem_original_require(path)
+      ensure
+        RUBYGEMS_ACTIVATION_MONITOR.enter
+      end
     end
 
     # If +path+ is for a gem that has already been loaded, don't
@@ -57,11 +62,16 @@ module Kernel
     #--
     # TODO request access to the C implementation of this to speed up RubyGems
 
-    spec = Gem::Specification.find { |s|
+    spec = Gem::Specification.stubs.find { |s|
       s.activated? and s.contains_requirable_file? path
     }
 
-    return gem_original_require(path) if spec
+    begin
+      RUBYGEMS_ACTIVATION_MONITOR.exit
+      return gem_original_require(path)
+    ensure
+      RUBYGEMS_ACTIVATION_MONITOR.enter
+    end if spec
 
     # Attempt to find +path+ in any unresolved gems...
 
@@ -109,11 +119,21 @@ module Kernel
       valid.activate
     end
 
-    gem_original_require path
+    begin
+      RUBYGEMS_ACTIVATION_MONITOR.exit
+      return gem_original_require(path)
+    ensure
+      RUBYGEMS_ACTIVATION_MONITOR.enter
+    end
   rescue LoadError => load_error
     if load_error.message.start_with?("Could not find") or
         (load_error.message.end_with?(path) and Gem.try_activate(path)) then
-      return gem_original_require(path)
+      begin
+        RUBYGEMS_ACTIVATION_MONITOR.exit
+        return gem_original_require(path)
+      ensure
+        RUBYGEMS_ACTIVATION_MONITOR.enter
+      end
     end
 
     raise load_error