Store username and url inside correct preference keys

I'm not sure how this happened. When I was testing, it worked for me, but perhaps I just ended up using an old value stored in the correct key. Sorry about that.

I noticed another problem. After "Verifying server" with correct username and password, I changed my password to something that is incorrect and tried verifying again. To my surprise, the verification passed. Looking at the debug output, I see (after disabling password obfuscation; also, actual email has been removed):
```
(3)(+0000007): HTTP OPTIONS for https://myEmail:wrongPassword@www.box.net/dav/test/zotero/

(3)(+0000397): Server: nginx
Date: Sun, 10 Feb 2013 09:24:01 GMT
Content-Type: httpd/unix-directory
Connection: keep-alive
X-Robots-Tag: noindex, nofollow
DAV: 1,2
Allow: GET, PUT, DELETE, MKCOL, OPTIONS, COPY, MOVE, PROPFIND, PROPPATCH, LOCK, UNLOCK, HEAD
MS-Author-Via: DAV
Content-Length: 0


(3)(+0000000): 

(3)(+0000000): ===>200<===(number)
```

It seems like it might be sending cookies with the OPTIONS request and what's worse is that the server essentially ignores the username and password if it gets a cookie (so I guess this is more of a box.net problem). It's a bit difficult to say for sure, since even if I try to go HTTP route, I get redirected to an HTTPS page, but I can see that cookies are in fact sent to the HTTP address. My quick search did not turn up any way to easily block these cookies.