Backport trunk revs 826506, 826520, 826528, 987498

sync htdigest with trunk to fix overflows and pick up other minor tweaks

Reviewed by: poirier, rpluem


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@999717 13f79535-47bb-0310-9956-ffa450edef68