Simplify umake.
Simplify umake.

	* sdk/umake.in (njobs): Not needed, use makeargs.
	Use +=.
	(defaultenv): Rename as URBI_ENV for consistency.
	(URBI_HOST): New, for consistency too.
	Use an envvar-overridable definition.

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