fix the keys adding 'portal_type_workflow_chain/'
in _importFile, preinstall and export."

This reverts commit 6f8221b6.

This commit cleaned inconsistent prefix manipulation in
PortalTypeWorkflowChainTemplateItem. It passes the test suite,
however it was found to produce incompatibility with previously installed
business templates. In 'Upgrade Business Templates from Repositories"
there was a diff of PortalTypeWorkflowChainTemplateItems like:
Portal Type Name -> New
portal_type_workflow_chain/Portal Type Name -> Removed
For some reason the upgrade process would remove the chain
without adding the new element.

We are working on a clean solution, but since this needs more testing
I revert this commit for now so that master version does not cause
problems to users.