Modularize ajax (and sub-modules).

Tests are guaranteed to run with ajax removed, not with just ajax/jsonp, ajax/script or ajax/xhr removed.
Removing ajax saves 3982 bytes minified gzipped.

grunt.js

@@ -64,10 +64,10 @@ module.exports = function( grunt ) {
 				"src/traversing.js",
 				"src/manipulation.js",
 				{ flag: "css", src: "src/css.js" },
-				"src/ajax.js",
-				"src/ajax/jsonp.js",
-				"src/ajax/script.js",
-				"src/ajax/xhr.js",
+				{ flag: "ajax", src: "src/ajax.js" },
+				{ flag: "ajax/jsonp", src: "src/ajax/jsonp.js", needs: [ "ajax", "ajax/script" ]  },
+				{ flag: "ajax/script", src: "src/ajax/script.js", needs: ["ajax"]  },
+				{ flag: "ajax/xhr", src: "src/ajax/xhr.js", needs: ["ajax"]  },
 				{ flag: "effects", src: "src/effects.js", needs: ["css"] },
 				{ flag: "offset", src: "src/offset.js", needs: ["css"] },
 				{ flag: "dimensions", src: "src/dimensions.js", needs: ["css"] },