Fix a but that lead to text modifications immediately after update
not always being detected.  Sleeping for 1ms is not sufficient for
some Linux filesystems that appear to have high resolution timestamps.

* subversion/libsvn_subr/io.c
  (svn_io_sleep_for_timestamps): Refactor to call sleep at the
   same place for all filesystems, increase sleep to 10ms for
   hi-res filesystems.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1581305 13f79535-47bb-0310-9956-ffa450edef68