Add 'zfs_member' to the list of supported filesystems.

git-svn-id: svn://svn.code.sf.net/p/openmediavault/code@1483 3c3d7b80-5828-415e-9f61-280b98178fff
Begin to improve OMVFilesystems class. The supported types can be enhanced via OMVFilesystems::register(). E.g.

require_once("openmediavault/system.inc");
OMVFilesystems::register("zfs_member", array("fstabent" => FALSE));

git-svn-id: svn://svn.code.sf.net/p/openmediavault/code@1484 3c3d7b80-5828-415e-9f61-280b98178fff