The st_mode field in struct stat is a bitfield of more than just the
file type, this commit masks off the non-filetype bits to ensure no
unrelated bits are checked.
Our `find` utility makes use of the `dirent::d_type` field for filtering
results, which `Core::DirIterator` didn't expose. So, now it does. :^)
We now store the name and type of the entry as the "next" value instead
of just the name. The type is exposed as a `DirectoryEntry::Type`
instead of a `DT_FOO` constant, so that we're not tied to posixy
systems, and because proper enums are nice. :^)
