Merge remote-tracking branch 'public/bug11553_024' into bug11553_025

Conflicts:
	src/or/channel.h

changes/bug11553

@@ -0,0 +1,15 @@
+  o Minor features:
+    - When we run out of usable circuit IDs on a channel, log only one
+      warning for the whole channel, and include a description of
+      how many circuits there were on the channel. Fix for part of ticket
+      #11553.
+
+
+  o Major features (performance):
+    - Avoid wasting cycles looking for usable circuit IDs. Previously,
+      when allocating a new circuit ID, we would in the worst case do a
+      linear scan over the entire possible range of circuit IDs before
+      deciding that we had exhausted our possibilities. Now, we
+      try 64 circuit IDs at random before deciding that we probably
+      won't succeed. Fix for a possible root cause of ticket
+      #11553.