Apply patch 823328 -- support for rfc 2617 digestion authentication.

The patch was tweaked slightly.  It's get a different mechanism for
generating the cnonce which uses /dev/urandom when possible to
generate less-easily-guessed random input.

Also rearrange the imports so that they are alphabetical and
duplicates are eliminated.

Add a few XXX comments about things left undone and things that could
be improved.