Avoid Rack security warning no secret provided

This avoids "SECURITY WARNING: No secret option provided to Rack::Session::Cookie."
* Strip nils from collections on JSON and XML posts. [CVE-2013-0155] * dealing with empty hashes. Thanks Damien Mathieu
CVE-2013-0156: Safe XML params parsing. Doesn't allow symbols or yaml.
bumping version
Merge branch '3-2-sec' into 3-2-secmerge

* 3-2-sec:
  bumping version
  CVE-2013-0156: Safe XML params parsing. Doesn't allow symbols or yaml.
  * Strip nils from collections on JSON and XML posts. [CVE-2013-0155] * dealing with empty hashes. Thanks Damien Mathieu
  Avoid Rack security warning no secret provided

Conflicts:
	actionpack/CHANGELOG.md
	activerecord/CHANGELOG.md
	activesupport/CHANGELOG.md
Merge rails/3-2-stable into 403/3-2-stable-with-session-marshal-fix