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This change fix a memory leak due to a Webkit bug:
https://github.com/ariya/phantomjs/issues/12903



Also:

- Whitelist only localhost and 127.0.0.1 in Capybara + JS specs
- Blacklist all requests to media such as images, videos, PDFs, CSVs etc.
- Log all the requests made.
Signed-off-by: Rémy Coutable <remy@rymai.me>