Add $EUDEV_RULES_DIRECTORY to the list of rules directories.

The old udev 182 supported $UDEV_CONFIG_FILE, which in turn allowed
the search path to be customized, but eudev no longer has this, hence
this hack.

--- eudev-1.9/src/udev/udev-rules.c	2014-09-13 10:21:59.615980259 +0200
+++ eudev-1.9/src/udev/udev-rules.c	2014-09-13 10:24:13.839976335 +0200
@@ -46,15 +46,11 @@
         };
 };
 
-static const char* const rules_dirs[] = {
+static const char* rules_dirs[] = {
         UDEV_CONF_DIR "/rules.d",
         UDEV_RULES_DIR,
-        "/run/udev/rules.d",
         UDEV_LIBEXEC_DIR "/rules.d",
-#ifdef HAVE_SPLIT_USR
-        "/lib/udev/rules.d",
-        "/usr/lib/udev/rules.d",
-#endif
+	NULL,			  /* placeholder for $EUDEV_RULES_DIRECTORY */
         NULL};
 
 struct udev_rules {
@@ -1637,6 +1633,9 @@
 
         udev_rules_check_timestamp(rules);
 
+	/* Allow the user to specify an additional rules directory.  */
+	rules_dirs[3] = getenv("EUDEV_RULES_DIRECTORY");
+
         r = conf_files_list_strv(&files, ".rules", NULL, rules_dirs);
         if (r < 0) {
                 log_error("failed to enumerate rules files: %s", strerror(-r));
