Add merge_helpers.sh

Change-Id: Ia11bf326b360a9845c8df65d386c239b7b3eb414

merge_helpers.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+
+upstream_latest_tag() {
+    git describe upstream/master --tags
+}
+upstream_previous_tag() {
+    git describe `upstream_latest_tag`~1 --tags
+}
+upstream_diff() {
+    local latest_tag=`upstream_latest_tag`
+    local previous_tag=`upstream_previous_tag`
+    git diff "$previous_tag".."$latest_tag" "$@"
+}