Add the old test suite to the grunt task for both local tests and CI

This relies on a hack to bypass the `mocha` detection by `grunt-mocha-phantomjs`.
The tests have to run in less than 10 seconds, which is unlikely to be problematic on current
hardware.

Alternatively, adding the following to tests/index.html also makes the old test suite compatible
with the mocha runner, but it entails loading `mocha`:

    <script src="../node_modules/mocha/mocha.js"></script>
    <script>
        mocha.setup("bdd")
        describe("dummy test", function(){
            it("is a dummy test to run the old test suite with grunt-mocha-phantomjs like the new one", function(){})
        })
        mocha.run()
    </script>

Gruntfile.js

@@ -95,7 +95,7 @@ module.exports = function (grunt) { // eslint-disable-line
 
 		mocha_phantomjs: { // eslint-disable-line camelcase
 			test: {
-				src: ["test/index.html"],
+				src: ["test/index.html", "tests/index.html"],
 				options: {
 					reporter: "dot"
 				}

tests/index.html

@@ -4,5 +4,11 @@
 <script src="mock.js"></script>
 <script src="../mithril.js"></script>
 <script src="mithril-tests.js"></script>
+<script>
+// shim for running the old test suite with grunt-mocha-phantomjs like the new one
+if ('callPhantom' in window) {
+    window.callPhantom({ testRunEnded: 1})
+}
+</script>
 
 <p>Open the console to see the test report</p>