Support quoted environment variables

This change makes use of shlex to correctly parse the environment options and work around quoted values. 

For example:

    Python 2.7.5 (default, May 15 2013, 22:43:36) [MSC v.1500 32 bit (Intel)] on win32
    Type "help", "copyright", "credits" or "license" for more information.
    >>> "QUEUEBOT_USERNAME=bot1@bot.pleaseignore.com QUEUEBOT_PASSWORD=\"Lines are awesome!!\"".split()
    ['QUEUEBOT_USERNAME=bot1@bot.pleaseignore.com', 'QUEUEBOT_PASSWORD="Lines', 'are', 'awesome!!"']
    >>> import shlex
    >>> shlex.split("QUEUEBOT_USERNAME=bot1@bot.pleaseignore.com QUEUEBOT_PASSWORD=\"Lines are awesome!!\"")
    ['QUEUEBOT_USERNAME=bot1@bot.pleaseignore.com', 'QUEUEBOT_PASSWORD=Lines are awesome!!']
    >>>