better error dialog on receiver permission error; fixes #17

The problem is caused by starting Solaar right after installing it; while udev
does have the new rule loaded, the /dev/hidraw* device nodes already exist
with the old permissions.

Rather than doing a "udevadm --reload-rules" (which could have unknown side-
effects on other devices), instruct the user to remove and re-insert the usb
receiver. The new /dev/hidraw* device nods will be created with the right
permissions.

lib/solaar/gtk.py

@@ -69,11 +69,12 @@ def _run(args):
 			except OSError:
 				# permission error, blacklist this path for now
 				listeners.pop(device.path, None)
-				import logging
-				logging.exception("failed to open %s", device.path)
-				# ui.error_dialog(window, 'Permissions error',
-				# 				'Found a possible Unifying Receiver device,\n'
-				# 				'but did not have permission to open it.')
+				GLib.idle_add(ui.error_dialog, 'Permissions error',
+					'Found a Logitech Unifying Receiver device,\n'
+					'but did not have permission to open it.\n'
+					'\n'
+					'If you\'ve just installed Solaar, try removing\n'
+					'the receiver and plugging it back in.')
 
 		# elif action == 'remove':
 		# 	# we'll be receiving remove events for any hidraw devices,

lib/solaar/ui/__init__.py

@@ -37,8 +37,8 @@ from gi.repository import GLib, Gtk
 GLib.threads_init()
 
 
-def error_dialog(window, title, text):
-	m = Gtk.MessageDialog(window, Gtk.DialogFlags.MODAL, Gtk.MessageType.ERROR, Gtk.ButtonsType.CLOSE, text)
+def error_dialog(title, text):
+	m = Gtk.MessageDialog(None, Gtk.DialogFlags.MODAL, Gtk.MessageType.ERROR, Gtk.ButtonsType.CLOSE, text)
 	m.set_title(title)
 	m.run()
 	m.destroy()