Remove incorrect docs.

Session class no longer has these methods.
Update docs referencing old style flash messages.
Update login code.

It was wrong.
Set user to session.
Merge pull request #1436 from ADmad/3.0

Updated info about AuthComponent's method changes and other general info
Merge pull request #1435 from cakephp/session-de-dupe

Update docs for session changes and FlashComponent
[fr] follow #1436

Updated info about AuthComponent's method changes and other general info
[fr] follow #1435

Update docs for session changes and FlashComponent
Added docs for conditionall allowEmpty and notEmpty
Use sed to replace /App/ with /src/

This covers most of the work that will need to be done to the docs for
the App -> src change in cakephp/app.
Update entities.rst

syntax error, unexpected '=>' (T_DOUBLE_ARROW)
Merge pull request #1438 from archanavhire/patch-4

Update entities.rst
Fix App/ -> src/

This fixes another big gob of paths for the recent App->src directory
changes in cakephp/app
Fix a few more directory references.
Update based on review feedback.

@ADmad caught a pile of mistakes that I missed.
[fr] follow #1438

Update entities.rst
[fr] rename folders

- App => src
- Test => tests
- Plugin => plugins
Fixing some extra src/ in paths
Fixing paths in installation instructions
Merge pull request #1439 from cakephp/app-src

Update App -> src