encode_utf7

# File lib/net/imap.rb, line 841
    def self.encode_utf7(s)
      return s.gsub(/(&)|([^\x20-\x25\x27-\x7e]+)/n) { |x|
        if $1
          "&-"
        else
          base64 = [u8tou16(x)].pack("m")
          "&" + base64.delete("=\n").tr("/", ",") + "-"
        end
      }
    end