HFS+: add custom dentry hash and comparison operations

Add custom dentry hash and comparison operations for HFS+ filesystems that are
case-insensitive and/or do automatic unicode decomposition.  The new
operations reuse the existing HFS+ ASCII to unicode conversion, unicode
decomposition and case folding functionality.

Signed-off-by: Duane Griffin <duaneg@dghda.com>
Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>