Merge pull request #26 from nyeholt/master

Fixed issue with too-aggressive caching causing errors with 404 publication
Fixed typo
BUGFIX set current site theme on security/login page
ADDED support for LinkMapping module
Developer identifiers static should use the Config:: system instead of a direct static reference. closes #28
ENHANCEMENT load editor.css into htmleditors based on active  site theme
MINOR define module directory path in _config
Merge branch 'master' of github.com:sheadawson/silverstripe-multisites
MINOR code commenting
Improved the way the assets subfolders are created and managed. Added documentation on this in the readme
Updated readme with xsite linking issue
FIX Don't cache the hostmap if there's no valid hosts entered for a Site object