Fix http directory traversal

The regular expression used to determine if a directory traversal succeeded assumes the server will respond with 1.1 and an OK message which is not a safe assumption at all.  I've change this to look for any HTTP 200 response.

Validation was against a system known vulnerable to http://www.exploit-db.com/exploits/12308/ and validated by hand.  Without this patch, modules/auxiliary/scanner/http/http_traversal.rb does not find the vuln.  With it, it does.