Repair CHECK_MAINTHREAD, and fix the consequences.
Repair CHECK_MAINTHREAD, and fix the consequences.

"if (a) pabort()" is *not* the same as "pasert(!a)" !

	* src/kernel/uobject.cc: Restore CHECK_MAINTHREAD,
	throw instead of asserting.
	(setTimer): Implement as an async call.
	(getUObject): Return 0 if safe attempt failed from
	an other thread instead of throwing.

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