Fix GCC 4.6's new -Wunused-but-set-variable warnings.

Most instances were dead code; for those, I removed the assignments.
Some were pieces of info we don't currently plan to use, but which
we might in the future.  For those, I added an explicit cast-to-void
to indicate that we know that the thing's unused.  Finally, one was
a case where we were testing the wrong variable in a unit test.
That one I fixed.

This resolves bug 3208.

changes/bug3208

@@ -2,3 +2,5 @@
     - Remove undocumented option "-F" from tor-resolve: it hasn't done
       anything since 0.2.1.16-rc.
 
+  o Minor bugfixes:
+    - Fix warnings from GCC 4.6's "-Wunused-but-set-variable" option.

src/or/circuitbuild.c

@@ -3766,7 +3766,6 @@ void
 entry_guards_compute_status(or_options_t *options, time_t now)
 {
   int changed = 0;
-  int severity = LOG_DEBUG;
   digestmap_t *reasons;
 
   if (! entry_guards)
@@ -3793,8 +3792,6 @@ entry_guards_compute_status(or_options_t *options, time_t now)
   if (remove_dead_entry_guards(now))
     changed = 1;
 
-  severity = changed ? LOG_DEBUG : LOG_INFO;
-
   if (changed) {
     SMARTLIST_FOREACH_BEGIN(entry_guards, entry_guard_t *, entry) {
       const char *reason = digestmap_get(reasons, entry->identity);

src/or/command.c

@@ -645,6 +645,7 @@ command_process_netinfo_cell(cell_t *cell, or_connection_t *conn)
 
   /* XXX maybe act on my_apparent_addr, if the source is sufficiently
    * trustworthy. */
+  (void)my_apparent_addr;
 
   if (connection_or_set_state_open(conn)<0)
     connection_mark_for_close(TO_CONN(conn));

src/or/control.c

@@ -3142,7 +3142,6 @@ control_event_circuit_status(origin_circuit_t *circ, circuit_status_event_t tp,
 {
   const char *status;
   char extended_buf[96];
-  int providing_reason=0;
   if (!EVENT_IS_INTERESTING(EVENT_CIRCUIT_STATUS))
     return 0;
   tor_assert(circ);
@@ -3166,7 +3165,6 @@ control_event_circuit_status(origin_circuit_t *circ, circuit_status_event_t tp,
     const char *reason_str = circuit_end_reason_to_control_string(reason_code);
     char *reason = NULL;
     size_t n=strlen(extended_buf);
-    providing_reason=1;
     if (!reason_str) {
       reason = tor_malloc(16);
       tor_snprintf(reason, 16, "UNKNOWN_%d", reason_code);

src/or/directory.c

@@ -1900,7 +1900,6 @@ connection_dir_client_reached_eof(dir_connection_t *conn)
             router_get_trusteddirserver_by_digest(conn->identity_digest);
           char *rejected_hdr = http_get_header(headers,
                                                "X-Descriptor-Not-New: ");
-          int rejected = 0;
           if (rejected_hdr) {
             if (!strcmp(rejected_hdr, "Yes")) {
               log_info(LD_GENERAL,
@@ -1913,7 +1912,6 @@ connection_dir_client_reached_eof(dir_connection_t *conn)
                * last descriptor, not on the published time of the last
                * descriptor.  If those are different, that's a bad thing to
                * do. -NM */
-              rejected = 1;
             }
             tor_free(rejected_hdr);
           }

src/or/dirvote.c

@@ -1592,7 +1592,7 @@ networkstatus_compute_consensus(smartlist_t *votes,
                      * is the same flag as votes[j]->known_flags[b]. */
     int *named_flag; /* Index of the flag "Named" for votes[j] */
     int *unnamed_flag; /* Index of the flag "Unnamed" for votes[j] */
-    int chosen_named_idx, chosen_unnamed_idx;
+    int chosen_named_idx;
 
     strmap_t *name_to_id_map = strmap_new();
     char conflict[DIGEST_LEN];
@@ -1610,7 +1610,6 @@ networkstatus_compute_consensus(smartlist_t *votes,
     for (i = 0; i < smartlist_len(votes); ++i)
       unnamed_flag[i] = named_flag[i] = -1;
     chosen_named_idx = smartlist_string_pos(flags, "Named");
-    chosen_unnamed_idx = smartlist_string_pos(flags, "Unnamed");
 
     /* Build the flag index. */
     SMARTLIST_FOREACH(votes, networkstatus_t *, v,

src/or/eventdns.c

@@ -1028,6 +1028,9 @@ request_parse(u8 *packet, ssize_t length, struct evdns_server_port *port, struct
 	GET16(answers);
 	GET16(authority);
 	GET16(additional);
+	(void)additional;
+	(void)authority;
+	(void)answers;
 
 	if (flags & 0x8000) return -1; /* Must not be an answer. */
 	flags &= 0x0110; /* Only RD and CD get preserved. */

src/test/test_crypto.c

@@ -69,7 +69,7 @@ test_crypto_rng(void)
     uint64_t big;
     char *host;
     j = crypto_rand_int(100);
-    if (i < 0 || i >= 100)
+    if (j < 0 || j >= 100)
       allok = 0;
     big = crypto_rand_uint64(U64_LITERAL(1)<<40);
     if (big >= (U64_LITERAL(1)<<40))
@@ -240,11 +240,13 @@ test_crypto_sha(void)
   /* Test SHA-1 with a test vector from the specification. */
   i = crypto_digest(data, "abc", 3);
   test_memeq_hex(data, "A9993E364706816ABA3E25717850C26C9CD0D89D");
+  tt_int_op(i, ==, 0);
 
   /* Test SHA-256 with a test vector from the specification. */
   i = crypto_digest256(data, "abc", 3, DIGEST_SHA256);
   test_memeq_hex(data, "BA7816BF8F01CFEA414140DE5DAE2223B00361A3"
                        "96177A9CB410FF61F20015AD");
+  tt_int_op(i, ==, 0);
 
   /* Test HMAC-SHA-1 with test cases from RFC2202. */