Remove unused variable.
Add new assert.

Not sure of this is still needed, but added it when I saw
empty headers being printed in debug output some time (after that it
never fired).
Indentation fix.
Bug fix in MergeIterator.

The result of this was that the same fd, when readable AND writable
was handled twice, which wasn't a problem. The only slightly negative
effect was that that caused 'ready', the return value of select(), to be
decremented by 2 extra, causing 1 or 2 other fds not to be handled that
loop (also not very serious).

I found this because the assert 'ready >= 0' fired, after substracting 2
from 'ready' while it had the value 1, which needs two fds to be active
at the same time: one being readable and writable and the other just
being readable or writable (happened maybe once per hour under heavy
load %-).
Add AICurlTimer::refresh

plus some minor improvements.
Add Curl*Pipeline* debug settings.

Added CurlPipelineConcurrentConnections, CurlMaxPipelineLength and
CurlPipelineMaxBodyStall (used in the next commit). Now also setting
the policy for concurrent connections (and pipeline length) when curl
detects pipelining - and not only when we do (that was a bug).
Add CurlEasyRequest::mBadConnectionTimer

Seems not as important as I thought, but well.
I once saw a server stall in the midst of sending data. If that happens
we can terminated that connection a lot faster than waiting 15 seconds.