Automatic export creates initialize item with illegal name for top-level same-name siblings

Automatic export creates initialize item with an illegal name for same-name siblings at the top-level of imported XML files.

Steps to reproduce:
1. start an archetype-created project; auto-export will be enabled by default
2. in the console, add two nodes called "test", both at root level. They will be auto-exported.
3. stop the project, rebuild (mvn verify) and start the repository again

Expected: no bootstrap errors
Actual: bootstrap errors!

The problem is that each "test" node gets its own initialize item, and the names of the initialize items end with the top-level node name. That gives initialize item names "myhippoproject-test" and "myhippoproject-test[2]". The bootstrap process than tries to create nodes below /hippo:configuration/hippo:initialize for each item, which fails for the second one because of the [2] suffix.