* lib/net/imap.rb (Net::IMAP#fetch): [DOC] Describe how a range in
  +set+ is interpreted, and mention -1 which can be used for '*'.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46512 b2dd03c8-39d4-4d8f-98ff-823fe69b080e