Possible upload timeout improvement.

When uploading finishes, but is not detected, the timeout should be for
"reply delay", the time that the server takes before it replies, and not
CurlTimeoutLowSpeedTime. This patch adds code that takes this failure
into account (which happened only ONCE for me on Metropolis while flying
around and using trickle (not sure if that is relevant), so it's not
that likely to improvement anything in practise. Note that it is
detected by an assertion when it happens, so that we can safely assume
it normally never happened on SL).

* Generalized PUT / POST configuration by adding
  CurlEasyRequest::setPut, which now also supports keep-alive (which
  still isn't used).
* Upload content length is now stored in CurlEasyRequest::mContentLength
* CurlEasyRequest::has_stalled() now return false if it was possbile
  that the 'upload finished' detect failed AND calls upload_finished()
  itself in that case, so it is no longer 'const'.
* If low speed is detect exactly when the last bytes are being attempted
  to be sent (unlikely scenario), then the upload gets 4 more seconds
  after which is switches to CurlTimeoutReplyDelay.
* Added EDoesAuthentication and EAllowCompressedReply to replace
  booleans, for readability and type-safety, as did EKeepAlive. Note
  that this change inverts the meaning of the compression related parameter.
* Unrelated: removed an unnecessary #include "llurlrequest.h" from
  llxmlrpcresponder.h
Lowered CurlTimeoutLowSpeedLimit from 56 kB/s to 7 kB/s.

This value really IS in bytes/s (not for the total), and apparently 56
kB/s is too optimistic. The value was used by LL for transfers that went
beyond the total download time (2 minutes?), adding enough seconds per
received bytes to the timeout to allow a download at 56 kB/s to finish.

Our meaning is different however: we time out immediately and whenever
the download drops below this speed.

Perhaps a better algorithm is where the speed demand is based on the
total size of the download, but I'm not sure we always know the size of
downloads at this point.
Update AIHTTPTimeoutPolicy objects when their base changes.

Actually propagate changes to CurlTimeout* Debug Settings to the timeout policy objects.