* lib/rexml/security.rb (REXML::Security): create.
* lib/rexml/rexml.rb: move entity_expansion_limit and
  entity_expansion_text_limit accessors to ...
* lib/rexml/security.rb: ... here.
* lib/rexml/document.rb: use REXML::Security.
* lib/rexml/text.rb: use REXML::Security.
* test/rexml/test_document.rb: use REXML::Security.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39528 b2dd03c8-39d4-4d8f-98ff-823fe69b080e