Fix some issues

Hi, while learning to use Selenium Grid Extras, I found some bugs that are fixed in this PR.
Two of them are blocker for me:

- After executing dir, ps or video commands, the Grid Extras server doesn't reply to more commands.
  There is a deadlock because waitFor method was called before reading the output and error streams.

- An exception is thrown by the node when setting an implicit wait with selenium-server 2.44.0: WebDriverException: Message: For input string: "5000.0"
  It's due to a conflict with gson library, selenium 2.44.0 needs gson 2.3 and Grid Extras have 2.2.2. I've updated gson from 2.2.2 to 2.3.