The HTTP/2 specification requires header names to be lower case.

by calling grpc_init on [GRPCCall load], instead of lazily.

I can’t wait to get all of these automatically from a single source :)

Also change grpcio-tools to be a runtime dependency of grpcio-tests,
grpcio-tools is run as part of the tests.

Also make the script fetch protoc from the usual place.