keyvalue: display field was saved instead of value field

git-svn-id: http://www.pimcore.org/svn/pimcore/private/core/trunk@2175 1f8fe7d8-47f0-464c-8d0a-336f4953ab05
fixed a couple of display field/value field related bugs

git-svn-id: http://www.pimcore.org/svn/pimcore/private/core/trunk@2176 1f8fe7d8-47f0-464c-8d0a-336f4953ab05
fixed bug in memcache adapter (insert on duplicate key update) tag -> id order was wrong

git-svn-id: http://www.pimcore.org/svn/pimcore/private/core/trunk@2177 1f8fe7d8-47f0-464c-8d0a-336f4953ab05