Retry page.click on relative link

Some erroneous web pages contains links like `<a title="What is SEO?" href="vocabulary/seo">SEO</a>`with relative **href**.

Assume tihs link is placed at `http://some.domain.com/vocabulary`. That means that mechanize tries `http://some.domain.com/vocabulary/vocabulary/seo` which ends up with 404 error.

Browsers use a different approach - they treat such href as absolute in case relative url fails.
That patch implements described approach.

Here is an example which fails without the patch 
```
require 'rubygems'
require 'bundler/setup'
require 'wombat'

class GithubScraper
  include Wombat::Crawler
  base_url "http://liteproblog.ru/"
  path "/vocabulary"

  vocabulary 'css=.postcontent ul li a', :follow do
    entry do
      word 'css=.post p strong', :text
      description 'css=.post p'
    end
  end
end
puts GithubScraper.new.crawl
```