Attempt to debug 259 exit code on AppVeyor

Let's try to dig in a bit more and see where this is coming from, it
looks like AppVeyor is also unsure where this is coming from!

src/ci/run.sh

@@ -121,7 +121,14 @@ fi
 travis_fold end log-system-info
 
 if [ ! -z "$SCRIPT" ]; then
+  # This `set +e` followed by capturing the return value is a temporary measure
+  # to help debug "error with exit 259" on AppVeyor temporarily, otherwise all
+  # that's needed here is the `sh`
+  set +e
   sh -x -c "$SCRIPT"
+  ret=$?
+  echo "script exited with $ret"
+  exit $ret
 else
   do_make() {
     travis_fold start "make-$1"