WebDAV file access notes

Short term:
 * Can use webdav to access the existing file/web server tree
 * HTTP auth and/or IP limitations on server
 * Should be possible to switch over access mode per-repo or per-wiki without breaking compat
 * If server doesn't respond, fail out quickly and gracefully!
 * May be necessary to reduce the frequency we actually hit the backing files

Long term:
 * Failover/clustering/etc needs?