Allow get_cookies to find comma separated cookies

While reviewing #3463 I've found the actual ```Rex::Proto::Http::Response::get_cookies``` is failing to find comma separated cookies, as set by applications like Splunk 5.0.1 on Windows 7 (32 bits). Example:

```
Set-Cookie: cval=880350187, session_id_8000=83466b1a1a7a27ce13d35f78155d40ca3a1e7a28; expires=Mon, 07 Jul 2014 20:09:28 GMT; httponly; Path=/, uid=348637C4-9B10-485A-BFA9-5E892432FCFD; expires=Fri, 05-Jul-2019 20:09:28 GMT
```

In the case above, ```get_cookies``` fails to find the ```cval``` cookie, because it's separated with a comma from ```session_id_8000```:

```
msf > irb
[*] Starting IRB shell...

>> res = Rex::Proto::Http::Response.new
=> HTTP/1.1 200 OK
Content-Length: 0
>>
?> response = <<-HEREDOC
HTTP/1.1 200 OK
Expires: Thu, 26 Oct 1978 00:00:00 GMT
Content-Length: 8556
Server: CherryPy/3.1.2
Date: Sun, 06 Jul 2014 20:09:28 GMT
Cache-Control: no-store, max-age=0, no-cache, must-revalidate
Content-Type: text/html;charset=utf-8
Set-Cookie: cval=880350187, session_id_8000=83466b1a1a7a27ce13d35f78155d40ca3a1e7a28; expires=Mon, 07 Jul 2014 20:09:28 GMT; httponly; Path=/, uid=348637C4-9B10-485A-BFA9-5E892432FCFD; expires=Fri, 05-Jul-2019 20:09:28 GMT
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<!--[if lt IE 7]> <html xmlns="http://www.w3.org/1999/xhtml" xmlns:s="http://www.splunk.com/xhtml-extensions/1.0" xml:lang="en" lang="en" class="no-js lt-ie9 lt-ie8 lt-
HEREDOC
=> "HTTP/1.1 200 OK\nExpires: Thu, 26 Oct 1978 00:00:00 GMT\nContent-Length: 8556\nServer: CherryPy/3.1.2\nDate: Sun, 06 Jul 2014 20:09:28 GMT\nCache-Control: no-store, max-age=0, no-cache, must-revalidate\nContent-Type: text/html;charset=utf-8\nSet-Cookie: cval=880350187, session_id_8000=83466b1a1a7a27ce13d35f78155d40ca3a1e7a28; expires=Mon, 07 Jul 2014 20:09:28 GMT; httponly; Path=/, uid=348637C4-9B10-485A-BFA9-5E892432FCFD; expires=Fri, 05-Jul-2019 20:09:28 GMT\n\n<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Strict//EN\" \"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd\">\n<!--[if lt IE 7]> <html xmlns=\"http://www.w3.org/1999/xhtml\" xmlns:s=\"http://www.splunk.com/xhtml-extensions/1.0\" xml:lang=\"en\" lang=\"en\" class=\"no-js lt-ie9 lt-ie8 lt-\n"
>>
?> res.parse(response)
=> 2
>>
?> res.get_cookies
=> "session_id_8000=83466b1a1a7a27ce13d35f78155d40ca3a1e7a28; uid=348637C4-9B10-485A-BFA9-5E892432FCFD;"
```

This patch tries to find the comma separated cookies:

```
msf > irb
[*] Starting IRB shell...

>> res = Rex::Proto::Http::Response.new
=> HTTP/1.1 200 OK
Content-Length: 0


>>
?> response = <<-HEREDOC
HTTP/1.1 200 OK
Expires: Thu, 26 Oct 1978 00:00:00 GMT
Content-Length: 8556
Server: CherryPy/3.1.2
Date: Sun, 06 Jul 2014 20:09:28 GMT
Cache-Control: no-store, max-age=0, no-cache, must-revalidate
Content-Type: text/html;charset=utf-8
Set-Cookie: cval=880350187, session_id_8000=83466b1a1a7a27ce13d35f78155d40ca3a1e7a28; expires=Mon, 07 Jul 2014 20:09:28 GMT; httponly; Path=/, uid=348637C4-9B10-485A-BFA9-5E892432FCFD; expires=Fri, 05-Jul-2019 20:09:28 GMT
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<!--[if lt IE 7]> <html xmlns="http://www.w3.org/1999/xhtml" xmlns:s="http://www.splunk.com/xhtml-extensions/1.0" xml:lang="en" lang="en" class="no-js lt-ie9 lt-ie8 lt-
HEREDOC
=> "HTTP/1.1 200 OK\nExpires: Thu, 26 Oct 1978 00:00:00 GMT\nContent-Length: 8556\nServer: CherryPy/3.1.2\nDate: Sun, 06 Jul 2014 20:09:28 GMT\nCache-Control: no-store, max-age=0, no-cache, must-revalidate\nContent-Type: text/html;charset=utf-8\nSet-Cookie: cval=880350187, session_id_8000=83466b1a1a7a27ce13d35f78155d40ca3a1e7a28; expires=Mon, 07 Jul 2014 20:09:28 GMT; httponly; Path=/, uid=348637C4-9B10-485A-BFA9-5E892432FCFD; expires=Fri, 05-Jul-2019 20:09:28 GMT\n\n<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Strict//EN\" \"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd\">\n<!--[if lt IE 7]> <html xmlns=\"http://www.w3.org/1999/xhtml\" xmlns:s=\"http://www.splunk.com/xhtml-extensions/1.0\" xml:lang=\"en\" lang=\"en\" class=\"no-js lt-ie9 lt-ie8 lt-\n"
>>
?> res.parse(response)
=> 2
>>
?> res.get_cookies
=> "cval=880350187; session_id_8000=83466b1a1a7a27ce13d35f78155d40ca3a1e7a28; uid=348637C4-9B10-485A-BFA9-5E892432FCFD;"
```

This regular expression isn't perfect to find cookies still, specially because is not able to find correctly values including commas. But hopefully it's better than before. Feedback is welcome. 
Ah, you are correct -- I misread this code.