Add improved timeout handling for HTTP transactions.

Introduces AIHTTPTimeoutPolicy objects which do not just
specify a single "timeout" in seconds, but a plethora of
timings related to the life cycle of the average HTTP
transaction.

This knowledge is that moved to the Responder being
used instead of floating constants hardcoded in the
callers of http requests. This assumes that the same
timeout policy is wanted for each transaction that
uses the same Responder, which can be enforced is needed.

I added a AIHTTPTimeoutPolicy for EVERY responder,
only to make it easier later to tune timeout values
and/or to get feedback about which responder runs
into HTTP errors in debug output (especially time outs),
so that they can be tuned later. If we already understood
exactly what we were doing then most responders could
have been left alone and just return the default timeout
policy: by far most timeout policies are just a copy
of the default policy, currently.

This commit is not finished... It's a work in progress
(viewer runs fine with it though).

indra/newview/app_settings/settings.xml

@@ -4227,16 +4227,82 @@
       <key>Value</key>
       <integer>256</integer>
     </map>
-    <key>CurlRequestTimeOut</key>
+    <key>CurlTimeoutDNSLookup</key>
     <map>
       <key>Comment</key>
-      <string>Max idle time of a curl request before killed (requires restart)</string>
+      <string>Extra time in seconds added to CurlTimeoutConnect for the initial connect to a host (requires restart)</string>
       <key>Persist</key>
       <integer>1</integer>
       <key>Type</key>
-      <string>F32</string>
+      <string>U32</string>
       <key>Value</key>
-      <real>120.0</real>
+      <real>60</real>
+    </map>
+    <key>CurlTimeoutConnect</key>
+    <map>
+      <key>Comment</key>
+      <string>Maximum time allowed until a connection is established (after adding the easy handle) until the server is considered unreachable and the connection is terminated (requires restart)</string>
+      <key>Persist</key>
+      <integer>1</integer>
+      <key>Type</key>
+      <string>U32</string>
+      <key>Value</key>
+      <real>10</real>
+    </map>
+    <key>CurlTimeoutReplyDelay</key>
+    <map>
+      <key>Comment</key>
+      <string>Maximum time the viewer will wait between sending data to the server and receiving (a partial) reply (requires restart)</string>
+      <key>Persist</key>
+      <integer>1</integer>
+      <key>Type</key>
+      <string>U32</string>
+      <key>Value</key>
+      <real>60</real>
+    </map>
+    <key>CurlTimeoutLowSpeedLimit</key>
+    <map>
+      <key>Comment</key>
+      <string>If a transfer speed drops below this value (in bytes/s) during CurlTimeoutLowSpeedTime seconds, the transfer is considered too slow and is terminated (requires restart)</string>
+      <key>Persist</key>
+      <integer>1</integer>
+      <key>Type</key>
+      <string>U32</string>
+      <key>Value</key>
+      <real>56000</real>
+    </map>
+    <key>CurlTimeoutLowSpeedTime</key>
+    <map>
+      <key>Comment</key>
+      <string>If a transfer speed drops below CurlTimeoutLowSpeedLimit (in bytes/s) during this amount of seconds, the transfer is considered too slow and is terminated (requires restart)</string>
+      <key>Persist</key>
+      <integer>1</integer>
+      <key>Type</key>
+      <string>U32</string>
+      <key>Value</key>
+      <real>30</real>
+    </map>
+    <key>CurlTimeoutMaxTransaction</key>
+    <map>
+      <key>Comment</key>
+      <string>Maximum total time of a curl transaction, from when the easy handle is added till the transaction has completed. This INCLUDES DNS lookups (CurlTimeoutConnect), connect time (CurlTimeoutConnect) and waiting for the first server reply (CurlTimeoutReply) as well as the actually time needed for data transfer (requires restart)</string>
+      <key>Persist</key>
+      <integer>1</integer>
+      <key>Type</key>
+      <string>U32</string>
+      <key>Value</key>
+      <real>300</real>
+    </map>
+    <key>CurlTimeoutMaxTotalDelay</key>
+    <map>
+      <key>Comment</key>
+	  <string>Maximum total time of a curl request, from when it is requested till the transaction has completed. This includes queuing due to connection throttling on top of the events covered by CurlTimeoutMaxTransaction (requires restart)</string>
+      <key>Persist</key>
+      <integer>1</integer>
+      <key>Type</key>
+      <string>U32</string>
+      <key>Value</key>
+      <real>600</real>
     </map>
     <key>Cursor3D</key>
     <map>