smbd: Simplify dropbox special case in unix_convert

EACCESS needs special treatment: If we want to create a fresh file,
return OBJECT_PATH_NOT_FOUND, so that the client will continue creating
the file. If the client wants us to open a potentially existing file,
we need to correctly return ACCESS_DENIED.

This patch makes this behaviour hopefully a bit clearer than the code
before did.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

Autobuild-User(master): Volker Lendecke <vl@samba.org>
Autobuild-Date(master): Mon Aug 26 12:14:26 CEST 2013 on sn-devel-104
Fix the erroneous masking of chmod requests via the UNIX extensions.

Changed from switch statement to if, as "create mask", "force create mode"
are only applied to new files, not existing ones. "directory mask",
"force directory mode" are only applied to new directories, not existing
ones.

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Simo Sorce <idra@samba.org>
Allow UNIX extensions client to act on open fsp instead of pathname if available.

Eliminates possible race condition on pathname op.

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Simo Sorce <idra@samba.org>
Fix the UNIX extensions CHOWN calls to use FCHOWN if available, else LCHOWN.

UNIX extensions calls must never deref links.

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Simo Sorce <idra@samba.org>

Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Mon Aug 26 20:19:46 CEST 2013 on sn-devel-104