Added http-host frontend param

This change add a 'http-host' parameter in the /data/params list of values.

The 'http-host' value is set to be the value of the HTTP_HOST constant.
Introducing General::intval()

This method will insure that we are really dealing with a positive integer before trying to cast it.

This should eliminate nasty side effects like casting '1234a' to 1234.
Use General::intval to cast system:id

This will make it safer and should fix #2191
Merge pull request #2136 from DeuxHuitHuit/current-domain

Added `http-host` page parameter
Fix typo in bundle.php
Merge pull request #2206 from DavidOliver/bundle-typo

Fix typo in bundle.php
Add missing quotes for Cache delete calls. Fixes #2202
Simplify the navigation item access for AdminstrationPage
Simplify parent/child navigation item creation
Release 2.5.1
Further optimisations to the Navigation building
Simplify logic in build page around checking for core/extension updates
Introduce Widget::Checkbox to automatically handle checkbox markup creation
Don't enforce the 'column' class for all Checkbox label's by default
Update to use Widget::Checkbox in the DSE/SE
Ensure anything modified in AddSectionElements delegate still works
Preserve CDATA nodes when converting XML string into XMLElement

CDATA was getting identified as DOMText and therefore sanitised when it should be preserved as a CDATA section.
Fix indentation
Merge pull request #2208 from g-wilson/integration

Preserve CDATA nodes when converting XML string into XMLElement
Added Status 302 header in redirect()

I do not know why, but without it, my setup was returning a 500 code if the actual http status was something else (404 in my case).

This fix only makes sure that the 302 status (temporary redirect) will be returned to the client.
After all, a call to redirect must really mean that we want a redirect.

Note: I did not used the Page class helpers since this is 'utility' code and I did not wanted to couple utility code to the Page class.