Adding a bunch of gulp utilities

This should allow a developer to write a gulpfile in TypeScript to
compile a TypeScript project.

gulp-if/gulp-if-tests.ts

@@ -0,0 +1,10 @@
+/// <reference path="./gulp-if.d.ts"/>
+/// <reference path="../gulp/gulp.d.ts"/>
+import gulp = require("gulp");
+import _if = require("gulp-if");
+
+gulp.src("test.css")
+    .pipe(_if(true, gulp.src("test.css")));
+
+gulp.src("test.css")
+    .pipe(_if(false, gulp.src("test.css"), gulp.src("test.css")));

gulp-if/gulp-if.d.ts

@@ -0,0 +1,11 @@
+// Type definitions for gulp-if
+// Project: https://github.com/robrich/gulp-if
+// Definitions by: Asana <https://asana.com>
+// Definitions: https://github.com/borisyankov/DefinitelyTyped
+
+/// <reference path="../node/node.d.ts"/>
+
+declare module "gulp-if" {
+    function gulpIf(condition: boolean, stream: NodeJS.ReadWriteStream, elseStream?: NodeJS.ReadWriteStream): NodeJS.ReadWriteStream;
+    export = gulpIf;
+}