Fix bug #2004 by demoting a log message.

To quote arma: "So instead of stopping your CBT from screaming, you're just
going to throw it in the closet and hope you can't hear it?"

Yep. The log message can happen because at 95% point on the curve, we can be
way beyond the max timeout we've seen, if the curve has few points and is
shallow.

Also applied Nick's rule of thumb for rewriting some other notice log messages
to read like how you would explain them to a raving lunatic on #tor who was
shouting at you demanding what they meant. Hopefully the changes live up to
that standard.

src/or/circuitbuild.c

@@ -258,8 +258,9 @@ circuit_build_times_new_consensus_params(circuit_build_times_t *cbt,
 
   if (num > 0 && num != cbt->liveness.num_recent_circs) {
     int8_t *recent_circs;
-    log_notice(LD_CIRC, "Changing recent timeout size from %d to %d",
-               cbt->liveness.num_recent_circs, num);
+    log_notice(LD_CIRC, "The Tor Directory Consensus has changed how many "
+               "circuits we must track to detect network failures from %d "
+               "to %d.", cbt->liveness.num_recent_circs, num);
 
     tor_assert(cbt->liveness.timeouts_after_firsthop);
 
@@ -592,8 +593,10 @@ circuit_build_times_shuffle_and_store_array(circuit_build_times_t *cbt,
 {
   int n = num_times;
   if (num_times > CBT_NCIRCUITS_TO_OBSERVE) {
-    log_notice(LD_CIRC, "Decreasing circuit_build_times size from %d to %d",
-               num_times, CBT_NCIRCUITS_TO_OBSERVE);
+    log_notice(LD_CIRC, "The number of circuit times that this Tor version "
+               "uses to calculate build times is less than the number stored "
+               "in your state file. Decreasing the circuit time history from "
+               "%d to %d.", num_times, CBT_NCIRCUITS_TO_OBSERVE);
   }
 
   /* This code can only be run on a compact array */
@@ -1074,7 +1077,7 @@ circuit_build_times_network_close(circuit_build_times_t *cbt,
     if (cbt->liveness.nonlive_timeouts == 1) {
       log_notice(LD_CIRC,
                  "Tor has not observed any network activity for the past %d "
-                 "seconds. Disabling circuit build timeout code.",
+                 "seconds. Disabling circuit build timeout recording.",
                  (int)(now - cbt->liveness.network_last_live));
     } else {
       log_info(LD_CIRC,
@@ -1158,7 +1161,7 @@ circuit_build_times_network_check_changed(circuit_build_times_t *cbt)
   control_event_buildtimeout_set(cbt, BUILDTIMEOUT_SET_EVENT_RESET);
 
   log_notice(LD_CIRC,
-            "Network connection speed appears to have changed. Resetting "
+            "Your network connection speed appears to have changed. Resetting "
             "timeout to %lds after %d timeouts and %d buildtimes.",
             tor_lround(cbt->timeout_ms/1000), timeout_count,
             total_build_times);
@@ -1296,7 +1299,7 @@ circuit_build_times_set_timeout_worker(circuit_build_times_t *cbt)
   }
 
   if (max_time < INT32_MAX/2 && cbt->close_ms > 2*max_time) {
-    log_notice(LD_CIRC,
+    log_info(LD_CIRC,
                "Circuit build measurement period of %dms is more than twice "
                "the maximum build time we have ever observed. Capping it to "
                "%dms.", (int)cbt->close_ms, 2*max_time);