feat(http): Add support for strings as http method names

Closes #4331

modules/angular2/src/http/http_utils.ts

@@ -1 +1,17 @@
+import {isString} from 'angular2/src/core/facade/lang';
+import {RequestMethods} from './enums';
+import {makeTypeError} from 'angular2/src/core/facade/exceptions';
+
+export function normalizeMethodName(method): RequestMethods {
+  if (isString(method)) {
+    var originalMethod = method;
+    method = method.replace(/(\w)(\w*)/g, (g0, g1, g2) => g1.toUpperCase() + g2.toLowerCase());
+    method = RequestMethods[method];
+    if (typeof method !== 'number')
+      throw makeTypeError(
+          `Invalid request method. The method "${originalMethod}" is not supported.`);
+  }
+  return method;
+}
+
 export {isJsObject} from 'angular2/src/core/facade/lang';