Change to allow special characters in passwords

This change to the aescrypt-gui script allows special characters (like spaces) in filenames and passwords. It uses a CPAN module to do the escaping.

note that because the password is passed via a command line arg and not through a pipe, we can't do anything with NUL characters (\000). It's unlikely anyone's going to hand us one, but it's a limitation.

Also makes it so that calls in the decrypt direction don't ask you to enter the password twice.