Disabled reporting detailed error messages from hub methods by default.

A generic error message now gets reported to invoking clients when a hub
method invocation fails.
Added unit tests to verify HubConfiguration settings work as intended.

Updated functional tests to enable detailed hub errors.
Updated the ASP.NET sample to enable detailed hub errors.
Renamed EnableDetailedHubErrors to EnableDetailedErrors
Removed redundant null checks in HubDispather.ProcessResponse
Functional test ensuring detailed hub errors are disabled by default