A nice error message when using shortcuts to change background_opacity without setting dynamic_background_opacity

Also change the default shortcuts

kittens/show_error/main.py

@@ -0,0 +1,46 @@
+#!/usr/bin/env python
+# vim:fileencoding=utf-8
+# License: GPL v3 Copyright: 2018, Kovid Goyal <kovid at kovidgoyal.net>
+
+import sys
+
+from kitty.cli import parse_args
+from ..tui.operations import styled
+
+
+OPTIONS = '''\
+--title
+default=ERROR
+The title for the error message.
+'''.format
+
+
+def real_main(args):
+    error_message = sys.stdin.buffer.read().decode('utf-8')
+    sys.stdin = open('/dev/tty')
+    msg = 'Show an error message'
+    args, items = parse_args(args, OPTIONS, '', msg, 'hints')
+    print(styled(args.title, fg_intense=True, fg='red', bold=True))
+    print()
+    print(error_message)
+    print()
+    input('Press Enter to close.')
+
+
+def main(args):
+    try:
+        real_main(args)
+    except KeyboardInterrupt:
+        pass
+    except Exception:
+        import traceback
+        traceback.print_exc()
+        input('Press Enter to close.')
+
+
+def handle_result(args, data, target_window_id, boss):
+    pass
+
+
+if __name__ == '__main__':
+    main(sys.argv)