Log Message:
math/djbsort: import djbsort-20180717

djbsort is a software library for sorting arrays of integers. It
provides the following features:

- Speed: djbsort holds new speed records for in-memory sorting.

- Security: djbsort is designed to be safe for cryptographic contexts.

- Verification: djbsort includes tools to automatically verify correctness.

These features are not separate options: there is a single sorting
function that is simultaneously fast, secure, and verified.

Packaged for wip by schmonz@