Added sanity check regarding i18n behavior when setting the Config.language property

$this->Session->read('Config.language) returns null when the property
doesn't exist in the Session object, and so sets the Config.language
property to null, overriding the default setting that was set by the
bootstrap file, as suggested in the previous paragraph.

Adding this simple sanity check ensures that no change is made to the
property if no locale information exists in the Session object.
Merge pull request #506 from PaulMougel/master

Added sanity check regarding i18n behavior when setting the Config.language property
Fixed the open search file for pages in "subcategories"
Added alternate link for others languages
Microdata for breadcrumbs
Merge pull request #508 from jrbasso/seo

Some SEO improvements
recursive tip
clarify recursive -1
Merge pull request #509 from dereuromark/master-recursive

recursive tip
Document magic postgres socket features.
Update form.rst

Remove Parenthesis from Form->inputDefaults example
Merge pull request #510 from ciccimanolesta/patch-1

Update form.rst
Minor corrections in the "Deployment" section
Merge pull request #512 from ataylor32/deployment-corrections

Minor corrections in the "Deployment" section
Minor corrections in the "Caching" section
Merge pull request #513 from ataylor32/caching-corrections

Minor corrections in the "Caching" section
small correction in fr/models.rst
Update french docs

Review of all commits from 01/03/2013 to 06/03/2013
Merge pull request #514 from cakephp-fr/master

Update of french docs