Setting dir_refresh or file_refresh to 0 does not ensure that a new GET/PROPFIND request is sent every time the file or
directory is opened. Instead the effective refresh interval is on average 0.5 seconds, because the refresh/retry is only
performed if the current time is greater than the refresh/retry deadline (not greater or equal) and the clock resolution
is 1 second.

In cache.c most time comparisons use the following logic:
    if (time(NULL) > deadline) {
         // do
    }
or
    if (time(NULL) <= deadline) {
        // skip
    }
so actions are only carried out once the time is one second past the deadline.

The attached patch only changes the comparisons in dav_statfs, update_directory and update_cache_file affected by the
dir_refresh and file_refresh variable but leaves over comparisons with the same pattern unchanged.

Note if the server does not support etags, the If-Modified-Since conditional GET request still only has 1 second
resolution.