minor fixes in shell scripts
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.