Fix #247: fall back to reboot -f in sulogin mode

When logged in from sulogin we cannot send IPC to Finit, not even
signals, to delegate reboot.  For usability, attempt to tell reboot that
it's in sulogin mode -- provided the bundled sulogin is used -- to let
reboot trigger over to forced reboot.

We cannot do much about initctl, just document this as a limitation.

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

doc/build.md

@@ -153,6 +153,9 @@ enabled.  The default Finit rescue mode configuration is installed into
 
 By default the a root shell, without login, is started.
 
+> **Note:** in this mode `initctl` will not work.  Use the `-f` flag to
+> force `reboot`, `shutdown`, or `poweroff`.
+
 
 Debugging
 ---------

doc/cmdline.md

@@ -63,7 +63,10 @@ The `bool` setting is one of `on, off, true false, 1, 0`.
     you will be given a root login to a maintenance shell.  However, if
     `sulogin` is missing, the file `/lib/finit/rescue.conf` is read and
     the system booted in a limited fallback mode.  See [config.md][]
-	for more information.
+    for more information.
+
+    **Note:** in this mode `initctl` will not work.  Correct the problem
+    and use `reboot -f` to force reboot.
 
 * `single`, or `S`: Single user mode, runlevel 1, in Finit.  Useful to
     debug problems with the regular runlevel.  All services and TTYs in

doc/config.md

@@ -645,6 +645,9 @@ activate it.
 
 The rescue mode comes in two flavors; *traditional* and *fallback*.
 
+> **Note:** in this mode `initctl` will not work.  Use the `-f` flag to
+> force `reboot`, `shutdown`, or `poweroff`.
+
 
 ### Traditional