mod_disk_cache: Retry file rename up to three times to ameliorate race

condition with htcacheclean removing the directories underneath us.

(Includes tweaks by Justin.)

Suggested by: Graham Leggett
Submitted by: Andreas Steinmetz <ast@domdv.de>
Reviewed by: Justin Erenkrantz


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@231349 13f79535-47bb-0310-9956-ffa450edef68