Stop trying to run more actions when one fails

Although many failures do simply die, there are some modes in which we
can fail to stop if an error occurs.  Fix these by sprinkling "|| exit"
judiciously in the command handling.

Signed-off-by: John Keeping <john@keeping.me.uk>
Fix error reporting if "git --exec-path" fails

Because we have not found and sourced git-sh-setup, we can't use "die"
here, so replace it with echo and exit.

Signed-off-by: John Keeping <john@keeping.me.uk>
Merge branch 'stop-if-action-fails'

Fix handling of certain error scenarios.

* stop-if-action-fails:
  Stop trying to run more actions when one fails
Merge branch 'fix-git-detect-error'

Don't use an undefined function if finding Git fails.

* fix-git-detect-error:
  Fix error reporting if "git --exec-path" fails