UX: Require verification of keyed password when using -p switch at command line

[unicorntoes]

What were you trying to do

Win32 - After entering the password prompt via -p switch, I was not able to verify I entered the correct password as age ran with the first password it was given. There is an opportunity to improve this behavior.

What happened

Age encrypted the file with the password keyed when prompted. Since there was no verification of the keyed password, I have no way of knowing if the password I entered was correct except to try to decrypt the file and test that the password keyed actually was keyed correctly.

<insert terminal transcript here>

[FiloSottile]

Duplicate of #39 which was fixed but not released. (I really need to make a release!)