compel: Add FIXME about --plugin-opts

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
libcompel: Rework command line options

 - Added "cflags","ldflags" actions
 - Support of -l,-L options
 - Packing multiple files
 - Added --plugin-args option (not yet handled)

Requested-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>