tests: work around strange mtime granularity issue on netbsd, fixes #204
tests: work around strange mtime granularity issue on netbsd, fixes #204

not sure where the problem is:
it seems to announce it supports st_mtime_ns, but if one uses it and
has a file with ...123ns, i t gets restored as ...000ns.

Then I tried setting st_mtime_ns_round to -3, but it still failed with +1000ns difference.

Maybe rounding is incorrect and it should be truncating?
Issue with granularity could be in python, in netbsd (netbsd platform code), in ffs filesystem, ...

edgewood/borg,mhubig/borg,edgimar/borg,mhubig/borg,edgimar/borg,edgimar/borg,RonnyPfannschmidt/borg,edgewood/borg,raxenak/borg,level323/borg,raxenak/borg,RonnyPfannschmidt/borg,RonnyPfannschmidt/borg,raxenak/borg,mhubig/borg,edgewood/borg,RonnyPfannschmidt/borg,edgewood/borg,edgimar/borg,level323/borg,level323/borg,RonnyPfannschmidt/borg,raxenak/borg