CSHARP-305: implemented new nuget packaging. MongoDB.Bson, MongoDB.Driver.Core, and MongoDB.Driver. Deprecated mongocsharpdriver.
changed a failing test to use the default write concern.
fixed issue where using camel case mapReduce command name does not exist on 2.6 and lower mongos.
fixed issue where unacknowledged write in test wasn't propogating fast enough causing a test to fail.
fixed issue where different versions of the server would cause the driver to throw different exceptions. Test for the old way proved we had fixed it but hadn't changed the tests.
fix issue with invalid nuspec package reference for the CI build.
added NuGetPush target to build file.