The GitRunner issue is resolved by running all the loaded Drama2 tasks form master

rather than ditsloadcmd loading them itself. This may be due to signal issues previously logged (death of child doesn't always get through on a modern Mac). I don't know why this suddenly started occurring in the Mojave runner and why things worked ok when I run manually on the same machine.

Modified imp such that Master no longer outputs error messages if a task it has loaded has died, in the case where transmitter is not running (our typical regression test case)