Convert sudo to use BSD TAILQ macros instead of home ground tail

queue functions.  This includes a private queue.h header derived
from FreeBSD.  It is simpler to just use our own header rather than
try to deal with macros that may or may not be present in various
queue.h incarnations.

common/sudo_conf.c

@@ -110,13 +110,14 @@ static struct sudo_conf_data {
     int group_source;
     int max_groups;
     const char *debug_flags;
-    struct sudo_conf_paths paths[5];
     struct plugin_info_list plugins;
+    struct sudo_conf_paths paths[5];
 } sudo_conf_data = {
     true,
     GROUP_SOURCE_ADAPTIVE,
     -1,
     NULL,
+    TAILQ_HEAD_INITIALIZER(sudo_conf_data.plugins),
     {
 #define SUDO_CONF_ASKPASS_IDX	0
 	{ "askpass", sizeof("askpass") - 1, _PATH_SUDO_ASKPASS },
@@ -302,10 +303,8 @@ set_plugin(const char *entry, const char *conf_file)
     info->symbol_name = estrndup(name, namelen);
     info->path = estrndup(path, pathlen);
     info->options = options;
-    info->prev = info;
-    /* info->next = NULL; */
     info->lineno = conf_lineno;
-    tq_append(&sudo_conf_data.plugins, info);
+    TAILQ_INSERT_TAIL(&sudo_conf_data.plugins, info, entries);
 }
 
 const char *