event: Ensure the event loop has been cleaned up in event_teardown

- Add input_teardown/signal_teardown to take care of closing signal/stdin
  handles.
- Call those functions in event_teardown, and ensure there are no active handles
  by entering an infinite loop when there are unclosed handles(think of this as
  an assertion that can't go unoticed on travis).
- Move event_teardown call to the end of mch_exit. That is required because
  event_poll may still be called in that function.

src/nvim/os/event.c

@@ -71,7 +71,15 @@ void event_teardown(void)
   channel_teardown();
   job_teardown();
   server_teardown();
+  signal_teardown();
   input_stop();
+  input_teardown();
+  do {
+    // This will loop forever if we leave any unclosed handles. Currently it is
+    // the most reliable way to use travis for verifying the no libuv-related
+    // bugs(which can be hard to track later) were introduced on a PR.
+    uv_run(uv_default_loop(), UV_RUN_DEFAULT);
+  } while (uv_loop_close(uv_default_loop()));
 }
 
 // Wait for some event

src/nvim/os/input.c

@@ -52,6 +52,15 @@ void input_init(void)
   rstream_set_file(read_stream, read_cmd_fd);
 }
 
+void input_teardown(void)
+{
+  if (embedded_mode) {
+    return;
+  }
+
+  rstream_free(read_stream);
+}
+
 // Listen for input
 void input_start(void)
 {

src/nvim/os/signal.c

@@ -55,6 +55,20 @@ void signal_init(void)
 #endif
 }
 
+void signal_teardown(void)
+{
+  signal_stop();
+  uv_close((uv_handle_t *)&sint, NULL);
+  uv_close((uv_handle_t *)&spipe, NULL);
+  uv_close((uv_handle_t *)&shup, NULL);
+  uv_close((uv_handle_t *)&squit, NULL);
+  uv_close((uv_handle_t *)&sterm, NULL);
+  uv_close((uv_handle_t *)&swinch, NULL);
+#ifdef SIGPWR
+  uv_close((uv_handle_t *)&spwr, NULL);
+#endif
+}
+
 void signal_stop(void)
 {
   uv_signal_stop(&sint);

src/nvim/os_unix.c

@@ -522,8 +522,6 @@ void mch_exit(int r)
 {
   exiting = TRUE;
 
-  event_teardown();
-
   {
     settmode(TMODE_COOK);
     mch_restore_title(3);       /* restore xterm title and icon name */
@@ -559,7 +557,7 @@ void mch_exit(int r)
   mac_conv_cleanup();
 #endif
 
-
+  event_teardown();
 
 #ifdef EXITFREE
   free_all_mem();