Before executing an action with multiple targets, we have to update every dependants of all targets of the actions.
(Not just the depenants of the target we're currently updating).
See //guest/miklos_fazekas/jamfix/testcases/multipletargetactions/Test.jam for an example of this problem.
>Test A B : C ;
>DEPENDS B : D ;
># Before executing Test A B : C, we should update D.