Filenames are not sanitized

```DEBUG:fuse.log-mixin:<- readdir ['.', '..', u'https://pasta.lternet.edu/package/data/eml/knb-lter-ntl/336/6/c4bc7ef43c78837ad066f8bb519f11ab', u'https://pasta.lternet.edu/package/report/eml/knb-lter-ntl/336/6']```

that of course results in cryptic FUSE errors