put a _ before or_options_t elements that aren't configurable

it's fine with me if we change the current convention, but we should
actually decide to change it if we want to.

src/or/config.c

@@ -713,7 +713,7 @@ or_options_free(or_options_t *options)
     return;
 
   routerset_free(options->_ExcludeExitNodesUnion);
-  tor_free(options->BridgePassword_AuthDigest);
+  tor_free(options->_BridgePassword_AuthDigest);
   config_free(&options_format, options);
 }
 
@@ -1310,8 +1310,8 @@ options_act(or_options_t *old_options)
                "BridgePassword.");
       return -1;
     }
-    options->BridgePassword_AuthDigest = tor_malloc(DIGEST256_LEN);
-    crypto_digest256(options->BridgePassword_AuthDigest,
+    options->_BridgePassword_AuthDigest = tor_malloc(DIGEST256_LEN);
+    crypto_digest256(options->_BridgePassword_AuthDigest,
                      http_authenticator, strlen(http_authenticator),
                      DIGEST_SHA256);
     tor_free(http_authenticator);

src/or/directory.c

@@ -3069,7 +3069,7 @@ directory_handle_command_get(dir_connection_t *conn, const char *headers,
   }
 
   if (options->BridgeAuthoritativeDir &&
-      options->BridgePassword_AuthDigest &&
+      options->_BridgePassword_AuthDigest &&
       connection_dir_is_encrypted(conn) &&
       !strcmp(url,"/tor/networkstatus-bridges")) {
     char *status;
@@ -3081,7 +3081,8 @@ directory_handle_command_get(dir_connection_t *conn, const char *headers,
 
     /* now make sure the password is there and right */
     if (!header ||
-        tor_memneq(digest, options->BridgePassword_AuthDigest, DIGEST256_LEN)) {
+        tor_memneq(digest,
+                   options->_BridgePassword_AuthDigest, DIGEST256_LEN)) {
       write_http_status_line(conn, 404, "Not found");
       tor_free(header);
       goto done;

src/or/or.h

@@ -2492,8 +2492,8 @@ typedef struct {
    * for bridge statuses -- but only if the requests use this password. */
   char *BridgePassword;
   /** If BridgePassword is set, this is a SHA256 digest of the basic http
-   * authenticator for it. */
-  char *BridgePassword_AuthDigest;
+   * authenticator for it. Used so we can do a time-independent comparison. */
+  char *_BridgePassword_AuthDigest;
 
   int UseBridges; /**< Boolean: should we start all circuits with a bridge? */
   config_line_t *Bridges; /**< List of bootstrap bridge addresses. */