Fixes an exploitable bug in CGI multipart parsing which affects Ruby <= 1.8.5.
When multipart boundary attributes contain non-halting regular
expression strings, the boundary searcher in the CGI module does not properly
escape the parameter and will execute arbitrary regular expressions.
This fix adds escaping for the user data.

    * Affected application servers: standalone CGI, Mongrel, WEBrick
    * Unaffected: FastCGI, Ruby 1.8.6 (all servers)
    * Unknown: mod_ruby

This fix will not modify versions of Ruby greater than 1.8.5, and is
cumulative with previous CGI multipart vulnerability fixes.