Upgrade to Selenium 2.21

v2.21.0
=======

WebDriver:
  * Safaridriver has now been added !
  * Issue 3489, maximize the browser window
  * Significant stability improvements in firefoxdriver.
  * Issue 3357 log-path for chromedriver
  * IE driver issue 3360
  * Android driver issue 3504
  * Firefox issue 3559, max-connections-per-server
  * Issue 3520
  * Issue 2826
  * Native events support for Firefox 11
  * Dropped native events support for Firefoxes 4-9

Grid:
  * Significant changes in the timeout strategy0 between hub, nodes and browser.
    See http://code.google.com/p/selenium/wiki/Grid2 section on timeouts.
    Compatibility note: It is recommended to at least update the nodes
    to 2.21. Upgrading only the hub will effectively disable the 
    browser-death timeout and is *not* recommended.
  * Improved error messages on console
  * Content length issue solved, Issue 2362
  * Issues 3328,3366
  * Improvements in thread dumps in both hub and node,
    possible to corrolate the two.
  * Added hub api to query parameters

Server:
  * -browserTimeout <timeoutInSeconds> added to
    differentiate between browser hang and client gone (which is
    -timeout <timeout>)
    - System property -Dselenium.server.timeout removed, use -timeout instead.
    See http://code.google.com/p/selenium/wiki/RemoteWebDriverServer 
    for further details.
    * Issue 3577