This INCOMPAT_LARGEDIR feature allows larger directories to be created
in ldiskfs, 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 current limit of approximately 10M entries in a
single directory.

This patch was originally written by Yang Sheng to support the Lustre server.

[ Bumped the credits needed to update an indexed directory -- tytso ]
Signed-off-by: NLiang Zhen <liang.zhen@intel.com>
Signed-off-by: NYang Sheng <yang.sheng@intel.com>
Signed-off-by: NArtem Blagodarenko <artem.blagodarenko@seagate.com>
Signed-off-by: NTheodore Ts'o <tytso@mit.edu>
Reviewed-by: NAndreas Dilger <andreas.dilger@intel.com>