Mark panic(), reset() and reboot() as noreturn
Add ext2_stat() with helper functions e.g. inode_for_path().

Still very messy, including copy/pasted code to read the directory
data; it uses the same code as ext2_lsdir (which isn't meant to be permanent),
though.
Quite a lot of ext2 cleanup.

I had three consecutive commits for "minor ext2 cleanup",
so I squished them; the result is a relatively major cleanup!
Add fstat() for ext2
Fix getdents! (This commit may be broken, splitting into multiple.)
Fix ext2_stat size for directories; add ext2_close (part was added in previous commit)
Update debug helper script
ls.c: show link count properly; user/group still hardcoded due to no kernel support yet
Comment out ext2 debug code
Split ext2_stat and make fstat more efficient (by not looking up the entire path for no reason).
Mark all internal ext2 functions as static