CustomUvar: use UVar.fill instead of cast.
CustomUvar: use UVar.fill instead of cast.

gcc had trouble handling convertion to std::string.

	* sdk-remote/include/urbi/customuvar.hxx (updateCache): Bounce
	to UVar.fill.

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