fix typo - missing word
typo - change  to
change headers example to use a request header (not a response header)
decorate php function with link to manual
add more descriptive text for book link
Shorten line under 80 chars
lower case request since it's not talking about the class
change to URI to be more consistent. fix typo. lower case Session
change query to request to be more accurate
lower case request
change final bullet to end with period
backtick Request. link to Request API
XML validation code needs constraint-mapping element

Missing XML information causes errors, has been been problematic for a while. See link for example: http://vvv.tobiassjosten.net/symfony/symfony2-validation-in-xml/
fix spelling
Create error_mapping.rst.inc

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | yes
| Applies to    | 2.1+
| Fixed tickets | ~

see http://symfony.com/blog/form-goodness-in-symfony-2-1#error-mapping-fu
added some more information about the security process
For BCrypt password encoder indicated PHP 5.5 is required
[#2715] Updating table format
Merge branch '2.1' into 2.2
Merge branch '2.2' into 2.3