Fixed geturl() function to ensure HEAD request method is used.

I came across this post [Feeds downloaded twice during update by update.php --feeds?](http://tt-rss.org/forum/viewtopic.php?f=1&t=2738) in the forums and based on some testing I did, it appears that when using open_basedir, curl was not actually using the HEAD method in `geturl()` when resolving URLs. I added the `CURLOPT_NOBODY`, which according to the [documentation](http://www.php.net/manual/en/function.curl-setopt.php) forces the HEAD method.

Further tests after this change showed that the HEAD method was now being used while resolving redirects.