Added a clear() function to Model.php (2.4 branch)

1.) Changed Pull Request from master branch to 2.4 (Old Pull Request: https://github.com/cakephp/cakephp/pull/1323)

2.) Updated return value in comment
Fix content-type header in cached views. Fixes issue #2358
Set content-type to xml to replicate existing behaviour
Remove trailing space
Update Model.php

fixed comment spacing
Fix test
Vanishing FULL_BASE_URL from the RouterTest
coding standards elseif
coding standards whitespace and single quote
more whitespace coding standard corrections
Merge pull request #1341 from dereuromark/master-coding-standards

Coding standards
incorrect tab to space - whitespace coding standards
Update version number to 2.3.6
Merge pull request #1342 from dereuromark/master-coding-standards

incorrect tab to space - whitespace coding standards
doc block
Minor optimization of CakeEmail::_wrap().
fix absolute url generation
Merge pull request #1343 from Phally/patch-1

Minor optimization of CakeEmail::_wrap().
Add forgotten exception class.

I forgot this in a previous set of commits, adding it now.
Fix failing tests in Network package.