additional storage tests
supress errors when using stat() on a non-existing file
better handling of partial cache data is getFileInfo
dont save data in the cache without mtime
dont use cache results without fileid in webdav
make webdav server work with .part files if they are explicitly requested
fix rename operation and touch on non existing file for webdav storage backend
remove error_log message
cache PROPFIND requests for 10 seconds, disable DIGEST auth for now, urlencode paths