relay MFR identifying header to OSF on auth
relay MFR identifying header to OSF on auth

 * WB had been sending it in the logging callback, but the auth
   endpoint is a more reliable tracking endpoint.  Every request needs
   auth, but not all requests log (e.g. if MFR already has the file
   cached)

RCOSDP/waterbutler,CenterForOpenScience/waterbutler,felliott/waterbutler