dispatch: fix silly blackbox entries when hg is interrupted When hg is interrupted, it creates ui.log like this: 1970/01/01 00:00:00 user @0000000000000000000000000000000000000000 (62488)> killed! exited 255 after 1.78 seconds This is due to a scoping problem: two different uses of the name "msg" collide. So rename one of them. Differential Revision: https://phab.mercurial-scm.org/D12427