hfsplus: add HFSX subfolder count support

Adds support for HFSX 'HasFolderCount' flag and a corresponding
'folderCount' field in folder records.  (For reference see
HFS_FOLDERCOUNT and kHFSHasFolderCountBit/kHFSHasFolderCountMask in
Apple's source code.)

Ignoring subfolder count leads to fs errors found by Mac:

  ...
  Checking catalog hierarchy.
  HasFolderCount flag needs to be set (id = 105)
  (It should be 0x10 instead of 0)
  Incorrect folder count in a directory (id = 2)
  (It should be 7 instead of 6)
  ...

Steps to reproduce:
 Format with "newfs_hfs -s /dev/diskXXX".
 Mount in Linux.
 Create a new directory in root.
 Unmount.
 Run "fsck_hfs /dev/diskXXX".

The patch handles directory creation, deletion, and rename.

Signed-off-by: Sergei Antonov <saproj@gmail.com>
Reviewed-by: Vyacheslav Dubeyko <slava@dubeyko.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>