ext4: Add support for non-native signed/unsigned htree hash algorithms

ext4: Add support for non-native signed/unsigned htree hash algorithms

(cherry picked from commit f99b25897a86fcfff9140396a97261ae65fed872)

The original ext3 hash algorithms assumed that variables of type char
were signed, as God and K&R intended.  Unfortunately, this assumption
is not true on some architectures.  Userspace support for marking
filesystems with non-native signed/unsigned chars was added two years
ago, but the kernel-side support was never added (until now).

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>