Consensus diff backend from Daniel Martí GSOC project.

(This commit was extracted by nickm based on the final outcome of
the project, taking only the changes in the files touched by this
commit from the consdiff_rebased branch.  The directory-system
changes are going to get worked on separately.)

src/common/log.c

@@ -1177,7 +1177,7 @@ static const char *domain_list[] = {
   "GENERAL", "CRYPTO", "NET", "CONFIG", "FS", "PROTOCOL", "MM",
   "HTTP", "APP", "CONTROL", "CIRC", "REND", "BUG", "DIR", "DIRSERV",
   "OR", "EDGE", "ACCT", "HIST", "HANDSHAKE", "HEARTBEAT", "CHANNEL",
-  "SCHED", "GUARD", NULL
+  "SCHED", "GUARD", "CONSDIFF", NULL
 };
 
 /** Return a bitmask for the log domain for which <b>domain</b> is the name,

src/common/torlog.h

@@ -101,8 +101,10 @@
 #define LD_SCHED     (1u<<22)
 /** Guard nodes */
 #define LD_GUARD     (1u<<23)
+/** Generation and application of consensus diffs. */
+#define LD_CONSDIFF  (1u<<24)
 /** Number of logging domains in the code. */
-#define N_LOGGING_DOMAINS 24
+#define N_LOGGING_DOMAINS 25
 
 /** This log message is not safe to send to a callback-based logger
  * immediately.  Used as a flag, not a log domain. */