Use GitHub search API to find updated repos.
Fix break caused by functionality change in net/url.

Handle
https://code.google.com/p/go/source/detail?r=03265149ced8e16074b7dbdb5e8a0a1d3f648fc5.

- Assume that String() prepends a '/' to the path.
- Escape fragment using URL.Fragment field. Although the code worked
  before, this is the correct way to escape a fragment.
Improve GitHub updates processing.

- Separate crawl queue from time for next crawl.
- Wait one hour before crawling recent updates to prevent flooding by
  frequently updated projects.