upgrade third_party/protobufs to 3.0.0-beta-1

src/csharp/.gitignore

src/csharp/Grpc.Examples.Tests/Grpc.Examples.Tests.csproj

src/csharp/Grpc.Examples.Tests/packages.config

src/csharp/Grpc.Examples/Grpc.Examples.csproj

src/csharp/Grpc.Examples/packages.config

...harp/Grpc.HealthCheck.Tests/Grpc.HealthCheck.Tests.csproj

src/csharp/Grpc.HealthCheck.Tests/packages.config

src/csharp/Grpc.HealthCheck/Grpc.HealthCheck.csproj

src/csharp/Grpc.HealthCheck/packages.config

...rp/Grpc.IntegrationTesting/Grpc.IntegrationTesting.csproj

src/csharp/Grpc.IntegrationTesting/packages.config

src/csharp/Grpc.Tools.nuspec

src/csharp/build_packages.bat

third_party/protobuf

tools/run_tests/run_sanity.sh

vsprojects/build_plugins.bat