Merge pull request #4476 from pks-t/pks/backport-script

scripts: add backporting script

script/backport.sh

+#!/bin/sh
+
+if test $# -eq 0
+then
+    echo "USAGE: $0 <#PR> [<#PR>...]"
+    exit
+fi
+
+commits=
+
+for pr in $*
+do
+    mergecommit=$(git rev-parse ":/Merge pull request #$pr" || exit 1)
+    mergebase=$(git merge-base "$mergecommit"^1 "$mergecommit"^2 || exit 1)
+
+    commits="$commits $(git rev-list --reverse "$mergecommit"^2 ^"$mergebase")"
+done
+
+echo "Cherry-picking the following commits:"
+git rev-list --no-walk --oneline $commits
+echo
+
+git cherry-pick $commits