Abort: kill all processes with SIGTERM

Since all directly launched processes are *bash* processes
we should use the trap option and send SIGTERM.

Previously, the merge and fetch phases would *not* be interrupted on
an abort.
Merge kill-git-commands-correctly (#62) into master

Abort: kill all processes with SIGTERM

Since all directly launched processes are *bash* processes
we should use the trap option and send SIGTERM.

Previously, the merge and fetch phases would *not* be interrupted on
an abort.