Add Pageant support to SftpDrive

I use PuTTY and SftpDrive a lot. PuTTY however has this excellent feature of keeping keeping private keys files loaded in memory through Pageant. When starting PuTTY or WinSCP they check with Pageant to see if any of the private keys work. If they do they connect automatically. The real catch is that the private key files can be encrypted on disk and are only decrypted once when pageant starts by asking you for a password. Thus allowing maximum security. Even if your PC or laptop gets stolen they still cant access your SSH servers. Since I use a laptop this is an issue for me.

If Pageant however cant be supported some similar method would also do.