gnu: Add emacs-gitpatch.

gnu: Add emacs-gitpatch.

By the way, “gitpatch.el” says different version than release tarball.
Do I need to ask a developer?
--8<---------------cut here---------------start------------->8---
;; Author: Feng Shu <tumashu@163.com>
;; Homepage: https://github.com/tumashu/gitpatch
;; Keywords: convenience
;; Package-Requires: ((emacs "24.3"))
;; Version: 0.10
--8<---------------cut here---------------end--------------->8---

>From 9eddf07fa401468738c2f48a25e51ddef2a3ceed Mon Sep 17 00:00:00 2001
From: Oleg Pykhalov <go.wigust@gmail.com>
Date: Sat, 29 Jul 2017 14:22:48 +0300
Subject: [PATCH] gnu: Add emacs-gitpatch.

* gnu/packages/emacs.scm (emacs-gitpatch): New variable.

Signed-off-by: Arun Isaac <arunisaac@systemreboot.net>