merge revision(s) 39721:

	* test/ruby/envutil.rb (EnvUtil.with_default_external): add for
	  changing Encoding.default_external without warnings.

	* test/ruby/envutil.rb (EnvUtil.with_default_internal): ditto.

	* test/ruby/test_io_m17n.rb: use above with_default_external.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@41364 b2dd03c8-39d4-4d8f-98ff-823fe69b080e