Small fixes

I had a problem when I used an alternate DONJONRC:
```
16:34:09 - crabman:(master)~/code/donjon >DONJONRC=/home/kim/.donjonrc2 bundle exec ./bin/dj init
/home/kim/code/donjon/lib/donjon/settings.rb:44:in `_load': undefined method `exist?' for "/home/kim/.donjonrc2":String (NoMethodError)
	from /home/kim/code/donjon/lib/donjon/settings.rb:32:in `get'
	from /home/kim/code/donjon/lib/donjon/settings.rb:21:in `method_missing'
	from /home/kim/code/donjon/lib/donjon/settings.rb:14:in `configured?'
	from /home/kim/code/donjon/lib/donjon/commands/vault.rb:15:in `init'
	from /home/kim/.gem/ruby/2.1.0/gems/thor-0.19.1/lib/thor/command.rb:27:in `run'
	from /home/kim/.gem/ruby/2.1.0/gems/thor-0.19.1/lib/thor/invocation.rb:126:in `invoke_command'
	from /home/kim/.gem/ruby/2.1.0/gems/thor-0.19.1/lib/thor.rb:359:in `dispatch'
	from /home/kim/.gem/ruby/2.1.0/gems/thor-0.19.1/lib/thor/base.rb:440:in `start'
	from /home/kim/code/donjon/lib/donjon/commands/base.rb:14:in `start'
	from ./bin/dj:5:in `<main>'
```

And if I choosed an own name, it wasn't saved:

```
17:15:21 - crabman:(master)~/code/donjon >bundle exec ./bin/dj init
Hi! How do you want to be called? [kim]
> defendor
Where do you want your vault? [~/.donjon]
> 
Do you want to use an existing private key or create one?
If you use an existing key, it needs to be an encrypted, 2048-bit RSA key.
Use [e]xisting or [c]reate?
> c
Where do you want to store your new key? [~/.ssh/donjon_rsa]
> 
Please enter a password for your new key (I won't store it anywhere)
> ******
Okay, that key seems valid.
Hi! How do you want to be called? [kim]
> defendor
Hi! How do you want to be called? [kim]
> defendor
Thanks! All your settings are saved.
17:15:40 + crabman:(master)~/code/donjon >cat ~/.donjonrc 
---
user_name: 
timestamp: 2014-07-14 17:15:40.780276509 +02:00
vault_path: "/home/kim/.donjon"
private_key: "/home/kim/.ssh/donjon_rsa"
```

Due to this the key was saved incorrect in `/home/kim/.donjon/users/.pub` instead of `/home/kim/.donjon/users/kim.pub`.


Both changes doesn't look very elegant to me. I just want to report them, feel free to make it nicer :)