Crawler checks if left domain by hostname.

Before this was done using `String.contains(x)`. However, that does not
work when in the new URL on another domain, the original domain is
passed through as a query parameter. Because the new method compares
hostnames, this cannot happen anymore.

Fixes #339
Merge pull request #357 from crawljax/fixes/339-crawler-escapes-domain

Crawler checks if left domain by hostname.