W3C detection

[robocoder]

The runtime detection hasn't been validated across a broad spectrum of drivers:

• https://github.com/instaclick/php-webdriver/blob/master/lib/WebDriver/Session.php#L128

Should we have a strict flag?

• if strict flag is false (default), obsolete methods are silently skipped (or emulated?)
• if strict flag is true, then obsolete/unknown methods will throw an exception, per AbstractWebDriver.php's getRequestMethod()

[mvorisek]

I think we can fire some request (execute request?) to detect W3C support on WebDriver creation.