Tweak git helper scripts

buildroot/share/git/mfrb

@@ -13,4 +13,8 @@ case "$#" in
   * ) echo "Usage: `basename $0`" 1>&2 ; exit 1 ;;
 esac
 
-git rebase -i ${INFO[3]}
+# If the branch isn't currently the PR target
+if [[ ${INFO[4]} != ${INFO[5]} ]]; then
+  git fetch upstream
+  git rebase upstream/${INFO[3]} && git rebase -i upstream/${INFO[3]}
+fi