* lib/rubygems: Update to RubyGems 2.4.1 master(713ab65)

Complete history at:
  https://github.com/rubygems/rubygems/blob/master/History.txt#L3-L216
* test/rubygems:  ditto.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47582 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rubygems/package/io_source.rb

@@ -0,0 +1,45 @@
+##
+# Supports reading and writing gems from/to a generic IO object.  This is
+# useful for other applications built on top of rubygems, such as
+# rubygems.org.
+#
+# This is a private class, do not depend on it directly. Instead, pass an IO
+# object to `Gem::Package.new`.
+
+class Gem::Package::IOSource < Gem::Package::Source # :nodoc: all
+
+  attr_reader :io
+
+  def initialize io
+    @io = io
+  end
+
+  def start
+    @start ||= begin
+      if io.pos > 0
+        raise Gem::Package::Error, "Cannot read start unless IO is at start"
+      end
+
+      value = io.read 20
+      io.rewind
+      value
+    end
+  end
+
+  def present?
+    true
+  end
+
+  def with_read_io
+    yield io
+  end
+
+  def with_write_io
+    yield io
+  end
+
+  def path
+  end
+
+end
+