New VFS module vfs_fruit

This module provides enhanced compatibility with Apple SMB clients and
interoperability with a Netatalk 3 AFP fileserver.

The module intercepts the OS X special streams "AFP_AfpInfo" and
"AFP_Resource" and handles them in a special way. All other named
streams are deferred to vfs_streams_xattr.

The OS X client maps all NTFS illegal characters to the Unicode
private range. This module optionally stores the charcters using their
native ASCII encoding.

Open modes are optionally checked against Netatalk AFP share modes.

The "AFP_AfpInfo" named stream is a binary blob containing OS X
extended metadata for files and directories. This module optionally
reads and stores this metadata in a way compatible with Netatalk 3
which stores the metadata in an EA "org.netatalk.metadata". Cf
source3/include/MacExtensions.h for a description of the binary blobs
content.

The "AFP_Resource" named stream may be arbitrarily large, thus it
can't be stored in an EA on most filesystem. ZFS on Solaris is an
exception to the rule, because it there EAs can be of any size and EAs
are first-class filesystem objects that can be used with normal file
syscalls like open(), read(), write(), fcntl() asf. This module stores
the AFP_Resource stream in an AppleDouble file, prepending "._" to the
filename. On Solaris and ZFS the stream is optionally stored in an EA
"org.netatalk.ResourceFork".

Signed-off-by: Ralph Boehme <rb@sernet.de>
vfs_fruit: add manpage

Signed-off-by: Ralph Boehme <rb@sernet.de>
s4-torture: add testsuite for VFS modules

Signed-off-by: Ralph Boehme <rb@sernet.de>
s4-torture: add testsuite for vfs_fruit

Signed-off-by: Ralph Boehme <rb@sernet.de>
wip: add test to selftest