IIS advanced log importing, netscaler log importing and cs-username handling

Includes changes to the log importer that should fix issues: #6795, #4707, #5980

@quba & @mattab can you take a look and see if these changes will provide the necessary features?
From http://support.microsoft.com/kb/944884:

> Beginning in IIS 6.0, the time-taken field typically includes network time. Before HTTP.sys logs the value in the time-taken field, HTTP.sys usually waits for the client to acknowledge the last response packet send operation or HTTP.sys waits for the client to reset the underlying TCP connection. Therefore, when a large response or large responses are sent to a client over a slow network connection, the value of the time-taken field may be more than expected. 

Will that be an issue if time-taken is used as average generation time?