Add check for file permissions on ~/.nipaprc

Ensure users don't leave easily readable .nipaprc file around
I think we should mimic SSH;
```
Permissions 0777 for '.ssh/id_rsa' are too open.
It is recommended that your private key files are NOT accessible by others.
This private key will be ignored.
```
Ie, drop the "Command failed" (anyone should get that much) and print "Permissions XXX for ~/.nipaprc are too open". I think this should be printed to stderr too. You should probably use string formatting for the path to the configuration file.