Fixed #2 - modified the AppConfigBase to default to using a null proxy
(instead of WebRequest.SystemWebProxy()) if the AdWordsApi config section
doesn't have a "ProxyServer" element. Using a null proxy will allow
System.Net.WebRequest to find a proxy if needed and to respect the
System.Net <defaultProxy enabled="false" /> app config setting
Merge pull request #4 from akilb/fix-appconfigbase-proxy

Fixed #2 - modified the AppConfigBase to default to using a null proxy if ProxyServer element not in AdWordsApi config section