* file.c (file_path_convert): don't convert it when the path string is
	  ascii only. [ruby-core:41556] [Bug #5733]
	  tests are contributed by nobu.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_3@36735 b2dd03c8-39d4-4d8f-98ff-823fe69b080e