- Reimplement $gif_interfaces as a variant of $cloned_interfaces.
  Newly-configured systems should use $cloned_interfaces.

- Call clone_{up,down}() and ifnet_rename() in rc.d/netif {start,stop}.
  ifnet_rename() now accepts an interface name list as its argument.

- Add rc.d/netif clear.  The "clear" subcommand is basically equivalent to
  "stop" but it does not call clone_down().

- Add "ifname:sticky" keyword into $cloned_interfaces.  If :sticky is
  specified, the interface will not be destroyed in rc.d/netif stop.

- Add cloned_interfaces_sticky={YES,NO}.  This variable globally sets
  :sticky keyword above for all interfaces.  The default value is NO.
  When cloned_interfaces_sticky=YES, :nosticky keyword can be used to
  override it on per interface basis.
Move the call to Job_SetPrefix() to Job_Init() so that
makefiles have had a chance to set .MAKE.JOB.PREFIX