Apply hotfix 3-2-null_array_param (CVE-2012-2694)

Array parameters should not contain nil values.

lib/action_dispatch/http/request.rb did not contain deep_munge nor parse_query methods.
I did only add deep_munge and parse_query.
parse_query does not seem to be called from somewhere else so this looks enough.

rake test are okay, so I hope the patch is fine.