Sicp kindle compat. & usability patches

Hi!

Here are a couple of patches which may or may not be useful. They're mostly updates for newer versions of things (ruby >1.9 and kindlegen 2.9) and usability changes (help texts, some failure analysis output).

This changeset also contains 2(!) patches for adding a hashbang to build_book.rb because I accidentally removed it again in f684b3a.

The patches are pretty *nix centric so if any of them pose a problem on Windows machines, I'm sorry.

Thanks for a nice little program!

Regards,
Anton