* 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/file_source.rb

@@ -0,0 +1,33 @@
+##
+# The primary source of gems is a file on disk, including all usages
+# internal to rubygems.
+#
+# This is a private class, do not depend on it directly. Instead, pass a path
+# object to `Gem::Package.new`.
+
+class Gem::Package::FileSource < Gem::Package::Source # :nodoc: all
+
+  attr_reader :path
+
+  def initialize path
+    @path = path
+  end
+
+  def start
+    @start ||= File.read path, 20
+  end
+
+  def present?
+    File.exist? path
+  end
+
+  def with_write_io &block
+    open path, 'wb', &block
+  end
+
+  def with_read_io &block
+    open path, 'rb', &block
+  end
+
+end
+