Test runner needs to add synthetic headers to raw request, too

[jhump]

These are extra headers used by the reference server, to verify that the client created the request in the expected way. They were previously only added to the structured request that normal clients use. But it also needs to be included in the raw request, for test cases that use raw requests with the reference client.

This also makes it so that the test case name header is always added, even when not running against the reference server. This is useful if tracing through and debugging an implementation -- you can easily tell which test case the request is for because it is always in the request headers.