use gnupg pinentry to accept password input

Hi Cosmin,

As you can see I'm bored.  And as you published some shell code I decided to make an improvement and add a safer password handling, pinentry.  pinentry is part of the GNUPG package, therefore it is considered safe.  It also has an ncurses screen for password input, which is nice.

The code is based on what the dyne.org guys use in the zsh tomb script, here: https://github.com/dyne/Tomb