* lib/fileutils.rb (FileUtils#symbolic_modes_to_i): Fix the wrong
  character class [+-=], which happened to match all desired
  characters but also match undesired characters.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41781 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* lib/fileutils.rb (FileUtils.chmod{,_R}): Enhance the symbolic
  mode parser to support the permission symbols u/g/o and multiple
  actions as defined in SUS, so that chmod("g=o+w", file) works as
  expected.  Invalid symbolic modes are now rejected with
  ArgumentError.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41782 b2dd03c8-39d4-4d8f-98ff-823fe69b080e