allow processes to handle hard interrupts

no general purpose api at this time

closes #2904

src/main/resources/assets/opencomputers/loot/openos/boot/01_process.lua

@@ -65,7 +65,8 @@ process.list[init_thread] = {
     vars={},
     handles={},
     io={}, --init will populate this
-    coroutine_handler = _coroutine
+    coroutine_handler = _coroutine,
+    signal = error
   },
   instances = setmetatable({}, {__mode="v"})
 }

src/main/resources/assets/opencomputers/loot/openos/lib/event.lua

@@ -36,7 +36,8 @@ computer.pullSignal = function(...) -- dispatch
   if interrupting then
     lastInterrupt = current_time
     if keyboard.isAltDown() then
-      error("interrupted", 0)
+      require("process").info().data.signal("interrupted", 0)
+      return
     end
     event.push("interrupted", current_time)
   end