windows: allow graceful shutdown on Windows, too

Until Etherpad 1.7.5, process.on('SIGTERM') and process.on('SIGINT') were not
hooked up under Windows, because old nodejs versions did not support them.
This excluded the possibility of doing a graceful shutdown of the database
connection under that platform.

According to nodejs 6.x documentation, it is now safe to do so. This allows to
gracefully close the DB connection when hitting CTRL+C under Windows, for
example.

Source: https://nodejs.org/docs/latest-v6.x/api/process.html#process_signal_events

  - SIGTERM is not supported on Windows, it can be listened on.
  - SIGINT from the terminal is supported on all platforms, and can usually be
    generated with <Ctrl>+C (though this may be configurable). It is not
    generated when terminal raw mode is enabled.

src/node/hooks/express/errorhandling.js

@@ -44,13 +44,27 @@ exports.expressCreateServer = function (hook_name, args, cb) {
     stats.meter('http500').mark()
   })
 
-  //connect graceful shutdown with sigint and uncaughtexception
+  /*
-  if(os.type().indexOf("Windows") == -1) {
+   * Connect graceful shutdown with sigint and uncaught exception
-    //sigint is so far not working on windows
+   *
-    //https://github.com/joyent/node/issues/1553
+   * Until Etherpad 1.7.5, process.on('SIGTERM') and process.on('SIGINT') were
+   * not hooked up under Windows, because old nodejs versions did not support
+   * them.
+   *
+   * According to nodejs 6.x documentation, it is now safe to do so. This
+   * allows to gracefully close the DB connection when hitting CTRL+C under
+   * Windows, for example.
+   *
+   * Source: https://nodejs.org/docs/latest-v6.x/api/process.html#process_signal_events
+   *
+   *   - SIGTERM is not supported on Windows, it can be listened on.
+   *   - SIGINT from the terminal is supported on all platforms, and can usually
+   *     be generated with <Ctrl>+C (though this may be configurable). It is not
+   *     generated when terminal raw mode is enabled.
+   */
   process.on('SIGINT', exports.gracefulShutdown);
+
   // when running as PID1 (e.g. in docker container)
   // allow graceful shutdown on SIGTERM c.f. #3265
   process.on('SIGTERM', exports.gracefulShutdown);
 }
-}