Show total rather than max

Unsure why previous code showed max of queued and active rather than the
total of the two.
Address comments

Reduce down to one counter variable.
Eliminate decrement at unqueue/increment at start request
Update counter emit aligned with counter increment/decrement.
Move decrement to end of request processing...

... to avoid counter going to zero and then up again.
Avoid wait until timer gets to zero ...

... to avoid delay if we are adding a request for a new host.
Merge pull request #162 from Sophist-UK/sophist_counter_throttle_tweak

Simplify and improve active requests counting