We now execute the validations when "kill" is executed even if match
criteria are used. This prevents users from killing workspace containers,
which instead kills all clients (as before when not using criteria).
fixes#1761
Previously, if a match specification contained the con_id or con_mark criterion,
all other criteria were ignored. However, a user may want to specify one of
those two unique identifiers and still specify others as well, for example to
match the currently focused window, but only if it has a certain WM_CLASS:
[con_id=__focused__ class=special] kill
We now check all specified criteria.
fixes#2111
