[MRG] Fix for #612 + small tests cleanup

Log looks like this now:

```
2014-03-19 03:56:30+0600 [scrapy] Crawled (402) <GET http://localhost:8998/status?n=402> (referer: None)
2014-03-19 03:56:30+0600 [scrapy] Ignoring response <402 http://localhost:8998/status?n=402>: HTTP status code is not handled or not allowed
```

I haven't put a test spider to scrapy.tests.spiders because it is unlikely be useful for other tests.

`docrawl` function was copy-pasted several times so I added it to scrapy.utils.test. In `test_crawl` crawler is now configured immediately instead of being configured via `yield defer.maybeDeferred(self.configure)` in `crawler.start()`, but it doesn't seem to affect anything.