Clang-format of changed files

Clean up anything that failed

Part of fixing https://github.com/grpc/grpc/issues/2192

The prefix has still to be applied per-message, and we could
do forward-declarations in the generated header.

Still missing: retrieving prefix from file option.

Move completion queue binding for new requests to the new request
request time, not server instantiation time.

By the standard, std::function can only capture class functions, and not
class methods. For some reasons, this works under gcc however. Visual
Studio rejects it. std::mem_fn is proper template to use.

It was awkward for the generated code to call an API that offered
both insecure_server and secure_server as well as insecure_stub and
secure_stub. With this change there is just a single server function
and a single stub function and security is decided based on arguments
passed.