ext2fs: temporarily disable htree directory index.

Our code does not consider yet the case of hash collisions. This
is a rather annoying situation where two or more files that
happen to have the same hash value will not appear accessible.

The situation is not difficult to work-around but given that things
will just work without enabling htree we will save possible
embarrassments for the next release.

Reported by:	Kevin Lo
newfs_msdos: fix inaccurate comments.

The fields from deMTime and deMDate in the DOS directory entry
are actually the last-modified time/date.

According to some online documentation these are the only
timestamps available in FAT12/FAT16.

MFC after:	3 days