Allow client to set `wd-url` setting.

In addition to specifiying the browsers to launch, allow the
client to pass along the WebDriver hub to use for launching.
Merge pull request #32 from reid/client-wd-url

Allow client to set `wd-url` setting.
Report for the correct test. Run once. Fix #129.

This commit fixes problems impacting Trac #129.

 - Results may be sent more than once from the browser.
   This can cause calls to next() in such as way that can
   duplicate test results for other URLs and cause
   running tests to stop and go to another test.
 - If results are sent twice, detect this and do not emit
   another results event for collection by the frontend.
 - Do not setExecuting(false) or setResults({}) for a
   scriptError, because we do not call next.
 - Move call to Agent#next after test results are recieved
   closer to the calls to setResults and setExecuting in
   the results agentEmitter handler.
Include requestMethod in RPC remote error message.
Prevent calling callback twice.

Return after the call to quit() to prevent the
callback from being called twice.
Allow 'internetexplorer' as a browser name.

For launching IE on buggy Selenium Hubs that don't accept the
standard "Internet Explorer" (with a space). This will be reverted
once we no longer need to launch on these buggy Hubs.
Nice errors for WebDriver launching.
Add proxy support for fetch_deps.
Remove special navigationTimeout for Android.

Does not appear to make a difference in testing YUI
for Android 2.3.4 on a Samsung Galaxy Tab.
Add DOH to website. Note Expect.js assertions.

- Expect.js assertions are needed for Mocha support, according
  to user reports.
- Link to DOH as "Dojo Objective Harness" since DOH is not a
  common acronym.
- Use the same order for supported frameworks in the README and site.
Yeti Blog -> Yeti on YUI Blog
Version 0.2.20.
Reduce arguments to connectAgent.
Add self-url.
When launching browsers, only test those browsers.

Do not use all agents connected to the Hub, instead use only
the browsers that were launched.
Restart browser API.
Consolidate forEach calls.
Work on 0.2.21pre.
Merge branch 'master' into wd-subset
Add Sauce Labs browsers.