e2fsprogs: add support for 3-level htree

e2fsprogs: add support for 3-level htree

The INCOMPAT_LARGEDIR feature allows larger directories to
be created, both with directory sizes over 2GB and and a
maximum htree depth of 3 instead of the current limit of 2.
These features are needed in order to exceed the currently
limit of approximately 10M entries in a single directory
for 4KB blocksize (~100k for 1KB).

debugfs, e2fsck, ext2fs, mke2fs and tune2fs support is
added.

Signed-off-by: Alexey Lyashkov <alexey.lyashkov@seagate.com>
Signed-off-by: Artem Blagodarenko <artem.blagodarenko@seagate.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>