Log Message:
Update libsigc++ to 2.2.10.
(while here, set test target.)

2.2.10:

* slot_rep: Avoid access to deleted object in notify(),
	and test case.
	(Kjell Ahlstedt ) Bug #564005 (Alexander Shaduri)
* Mention visit_each() in the documentation of sigc::adapts.
  (Thomas Rydzynski)