Make the path options required and use /tmp

Otherwise it's impossible to run this module without setting the options
which were not otherwise validated anyway.

modules/auxiliary/server/tftp.rb

@@ -5,6 +5,7 @@
 
 require 'msf/core'
 require 'rex/proto/tftp'
+require 'tmpdir'
 
 class Metasploit3 < Msf::Auxiliary
 
@@ -17,7 +18,7 @@ class Metasploit3 < Msf::Auxiliary
       'Description'    => %q{
         This module provides a TFTP service
       },
-      'Author'      => [ 'jduck' ],
+      'Author'      => [ 'jduck', 'todb' ],
       'License'     => MSF_LICENSE,
       'Actions'     =>
         [
@@ -34,8 +35,8 @@ class Metasploit3 < Msf::Auxiliary
       [
         OptAddress.new('SRVHOST',   [ true, "The local host to listen on.", '0.0.0.0' ]),
         OptPort.new('SRVPORT',      [ true, "The local port to listen on.", 69 ]),
-        OptString.new('TFTPROOT',   [ false,  "The TFTP root directory to serve files from" ]),
-        OptString.new('OUTPUTPATH', [ false, "The directory in which uploaded files will be written." ])
+        OptString.new('TFTPROOT',   [ true, "The TFTP root directory to serve files from", Dir.tmpdir  ]),
+        OptString.new('OUTPUTPATH', [ true, "The directory in which uploaded files will be written.", Dir.tmpdir ])
       ], self.class)
   end