Update sigaction to help address #1262.

Update example to have 4 cases - case 3 was previously broken but should
now work.

examples/sigaction.janet

@@ -1,11 +1,41 @@
-(defn action []
-  (print "cleanup")
+###
+### Usage: janet examples/sigaction.janet 1|2|3|4 &
+###
+### Then at shell: kill -s SIGTERM $!
+###
+
+(defn action
+  []
+  (print "Handled SIGTERM!")
+  (flush)
   (os/exit 1))
 
-(defn main [_]
-  # Set the interrupt-interpreter argument to `true` to allow
-  # interrupting the busy loop `(forever)`. By default, will not
-  # interrupt the interpreter.
+(defn main1
+  []
   (os/sigaction :term action true)
-  (os/sigaction :int action true)
   (forever))
+
+(defn main2
+  []
+  (os/sigaction :term action)
+  (forever))
+
+(defn main3
+  []
+  (os/sigaction :term action true)
+  (forever (ev/sleep math/inf)))
+
+(defn main4
+  []
+  (os/sigaction :term action)
+  (forever (ev/sleep math/inf)))
+
+(defn main
+  [& args]
+  (def which (scan-number (get args 1 "1")))
+  (case which
+    1 (main1) # should work
+    2 (main2) # will not work
+    3 (main3) # should work
+    4 (main4) # should work
+    (error "bad main")))

src/core/os.c

@@ -827,6 +827,7 @@ static void janet_signal_callback(JanetEVGenericMessage msg) {
     JanetFiber *fiber = janet_fiber(handler, 64, 0, NULL);
     janet_schedule(fiber, janet_wrap_nil());
     if (msg.argi) {
+        janet_vm.auto_suspend = 0; /* Undo interrupt if it wasn't needed. */
         janet_ev_dec_refcount();
     }
 }