Tolerate relative paths for torrc files with RunAsDaemon

We had a check to block these, but the patch we merged as a1c1fc72
broke this check by making them absolute on demand every time we
opened them.  That's not so great though. Instead, we should make them
absolute on startup, and not let them change after that.

Fixes bug 13397; bugfix on 0.2.3.11-alpha.

changes/bug13397

@@ -0,0 +1,4 @@
+  o Minor bugfixes:
+    - Avoid crashing when trying to reload a torrc specified as a relative
+      path with RunAsDaemon turned on.  Fixes bug 13397; bugfix on
+      0.2.3.11-alpha.

src/or/config.c

@@ -2584,11 +2584,6 @@ options_validate(or_options_t *old_options, or_options_t *options,
       REJECT("Failed to resolve/guess local address. See logs for details.");
   }
 
-#ifndef _WIN32
-  if (options->RunAsDaemon && torrc_fname && path_is_relative(torrc_fname))
-    REJECT("Can't use a relative path to torrc when RunAsDaemon is set.");
-#endif
-
   if (server_mode(options) && options->RendConfigLines)
     log_warn(LD_CONFIG,
         "Tor is currently configured as a relay and a hidden service. "
@@ -4152,14 +4147,17 @@ load_torrc_from_disk(config_line_t *cmd_arg, int defaults_file)
   int ignore_missing_torrc = 0;
   char **fname_var = defaults_file ? &torrc_defaults_fname : &torrc_fname;
 
-  fname = find_torrc_filename(cmd_arg, defaults_file,
-                              &using_default_torrc, &ignore_missing_torrc);
-  tor_assert(fname);
+  if (*fname_var == NULL) {
+    fname = find_torrc_filename(cmd_arg, defaults_file,
+                                &using_default_torrc, &ignore_missing_torrc);
+    tor_assert(fname);
+    tor_free(*fname_var);
+    *fname_var = fname;
+  } else {
+    fname = *fname_var;
+  }
   log_debug(LD_CONFIG, "Opening config file \"%s\"", fname);
 
-  tor_free(*fname_var);
-  *fname_var = fname;
-
   /* Open config file */
   if (file_status(fname) != FN_FILE ||
       !(cf = read_file_to_str(fname,0,NULL))) {