FileUtils.rmdir use remove_tailing_slash

* lib/fileutils.rb (FileUtils.rmdir): use remove_tailing_slash.
* test/fileutils/test_fileutils.rb: test for above.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41052 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2013-06-04

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41053 b2dd03c8-39d4-4d8f-98ff-823fe69b080e