userver: catch SIGINT in 3 steps to shutdown urbi.
userver: catch SIGINT in 3 steps to shutdown urbi.

	* src/kernel/userver.cc: Here.

aldebaran/urbi,aldebaran/urbi,aldebaran/urbi,urbiforge/urbi,urbiforge/urbi,urbiforge/urbi,urbiforge/urbi,aldebaran/urbi,aldebaran/urbi,aldebaran/urbi,urbiforge/urbi,aldebaran/urbi,urbiforge/urbi,urbiforge/urbi,urbiforge/urbi,urbiforge/urbi,aldebaran/urbi