Refactor: introduce telinit and a new initctl tool w/ API

- Reduce size of `helpers.c`, for linking against new `initctl` tool,
  by moving out functions to `pid.c` and `exec.c`
- Add `AF_UNIX` API to Finit, to complement old `/dev/initctl` FIFO
- Let old FIFO API be used by init/telinit: `init <q | 1-9>`
- Move all advanced initctl code from `client.c` to `initctl.c`, yes
  its a bit confusing to call the *new* tool the same as the old FIFO
  but this is more in line with what, e.g Upstart does.
- Move all advanced server side code from `plugins/initctl.c` to `api.c`
- Update TODO with upcoming inetd syntax change and dynamic events.
- Temporarily fix display of inetd services from `initctl status -v`

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

finit.h

@@ -73,6 +73,9 @@
 #define LINE_SIZE               1024
 #define BUF_SIZE                4096
 
+/* We reuse the INIT_CMD_ for the new initctl tool, but telinit only
+ * supports changing runlevel and reloading the configuration. */
+#define INIT_SOCKET             _PATH_VARRUN "finit.sock"
 #define INIT_MAGIC              0x03091969
 #define INIT_CMD_RUNLVL         1
 #define INIT_CMD_DEBUG          2    /* Toggle Finit debug */
@@ -81,6 +84,7 @@
 #define INIT_CMD_STOP_SVC       5
 #define INIT_CMD_RELOAD_SVC     6    /* SIGHUP service */
 #define INIT_CMD_RESTART_SVC    7    /* STOP + START service */
+#define INIT_CMD_QUERY_INETD    8
 #define INIT_CMD_NACK           254
 #define INIT_CMD_ACK            255