[ENH] Improved error reporting when the primary key is not defined in the schema

git-svn-id: file:///var/local/code.tiki.org/tikisvn/trunk@52803 b456876b-0849-0410-b77d-98878d47e9d5
[MOD] Allow to export auto-increment fields, move the rendering logic to the rendering phase to avoid data corruption

git-svn-id: file:///var/local/code.tiki.org/tikisvn/trunk@52804 b456876b-0849-0410-b77d-98878d47e9d5
[MOD] Adding import/export for single selection category field

git-svn-id: file:///var/local/code.tiki.org/tikisvn/trunk@52805 b456876b-0849-0410-b77d-98878d47e9d5