Print out *REQUEST* headers, not response, duh!
Allow behavior for excess requests to be control by the values of an environment variable,
PROTECTOR_OVERCAPACITY.
If unset or PROTECTOR_OVERCAPACITY=200, then we let everything through (eventually, as one of the
five slots frees up).
If PROTECTOR_OVERCAPACITY=503, then we only let 75 at a time sit around (including what's being processed);
more than that, and those requests get turned away immediately with error 503s (Service Unavailable)
Note that since the harness.go (test client program) throws 100 requests at whichever server it's pointed
at, we can count on certain numbers in tests, e.g., if PROTECTOR_OVERCAPACITY=503, 25 will have that return
status, while 75 will be allowed in
Changed format of output to log, changed environment variable to hold an alternate
URL rather than a "yes" (which actually has more hazards) was a little more verbose
in the comment, especially to the routine that make requests and gets replies regard
how it handled concurrency.