procdesc: add parameter name for stub procdesc_exit
capsicum: simplify path processing

Remove unnecessary duplication of flags field, and instead
use the version stored in nameidata->flags.  This removes
the need to pass around an extra parameter through all the
path processing code, and also means that the flags field
can be passed to path_init by value.

Also disallow nd_jump_link in O_BENEATH mode.