Library/Homebrew/test: add testbottest formula/tarball.

Minimal C program and Makefile used for testing Homebrew.

Library/Homebrew/test/testbottest.rb

+class Testbottest < Formula
+  desc "Minimal C program and Makefile used for testing Homebrew."
+  homepage "https://github.com/Homebrew/brew"
+  url "file://#{File.expand_path("..", __FILE__)}/tarballs/testbottest-0.1.tbz"
+  sha256 "78b54d8f31585c9773bed12b4aa4ab2ce458ebd044b9406cb24d40aa5107f082"
+
+  def install
+    system "make", "install", "PREFIX=#{prefix}"
+  end
+
+  test do
+    assert_equal "testbottest\n", shell_output("#{bin}/testbottest")
+  end
+end