Merge branch 'sb/submodule-parallel-fetch'

Simplify the two callback functions that are triggered when the
child process terminates to avoid misuse of the child-process
structure that has already been cleaned up.

* sb/submodule-parallel-fetch:
run-command: do not pass child process data into callbacks

diff --cc run-command.c
Simple merge

diff --cc run-command.h
Simple merge

diff --cc submodule.c
Simple merge