Test for generic 200 catch-all responses in web/dir_enum

[postmodern]

Some web servers will return a generic 200 response for every requested path. The web/dir_enum worker should first make a random request for a page that definitely won't exist (random alpha-numeric path). If it receives a valid 200 response, then all additional requests that return status 200 should compare their response bodies to the first catch-all response. This will help filter out catch-all web servers.