jruby - when XSD has DOCTYPE to DTD, not able to load the file.

in a clone of ruby-saml, running under jruby fails.

Found that some of the XSD files have DOCTYPE to DTD, and that was causing issues.

and the ruby script is run without path, NullPointerException got thrown.


```ruby
require 'rubygems'
require 'nokogiri'

Dir.chdir('lib/schemas') do
	Nokogiri::XML::Schema(IO.read('saml20protocol_schema.xsd'))
end
```