Allow the configuration file to be specified via an environment variable.

--- geoclue-2.1.10/src/gclue-config.c	2015-04-07 09:50:07.721074380 +0200
+++ geoclue-2.1.10/src/gclue-config.c	2015-04-07 10:27:26.613171960 +0200
@@ -235,6 +235,11 @@
 gclue_config_init (GClueConfig *config)
 {
         GError *error = NULL;
+	const char *config_file_path;
+
+	config_file_path = g_getenv ("GEOCLUE_CONFIG_FILE");
+	if (config_file_path == NULL)
+	  config_file_path = CONFIG_FILE_PATH;
 
         config->priv =
                 G_TYPE_INSTANCE_GET_PRIVATE (config,
@@ -242,7 +247,7 @@
                                             GClueConfigPrivate);
         config->priv->key_file = g_key_file_new ();
         g_key_file_load_from_file (config->priv->key_file,
-                                   CONFIG_FILE_PATH,
+                                   config_file_path,
                                    0,
                                    &error);
         if (error != NULL) {