* doc/syntax/control_expressions.rdoc:  Omit optional "then" for if and
  unless expressions.  Improved description of "a if a = 0.zero?"
  NameError.  Note that "do" for for loop is optional.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38844 b2dd03c8-39d4-4d8f-98ff-823fe69b080e