Global settings and PBKDF2 basically done

Global settings and the PBKDF2 are basically done. Global settings needs to jump to the right mode (tag or file).

As for PBKDF2, I just wrote the function; I haven't used it, yet.

Since this part of the project might benefit other Amazon S3 applications, I'm releasing the PBKDF2 source code under a BSD license to help other developers, S3 or otherwise, and to show how your account information is protected. Wikipedia gives a good overview of PBKDF2, for those who are interested.