bzr-svn follow a change of svn layout repository / missing history before restructurering

[Olivier R-D]

doing a test with a simple subversion directory confirms that going to a 
root layout to a trunk layout seems to confuse bzr-svn.
bzr-svn misses all history before the layout change and doing a merge 
with existing bzr branch does not seem possible.

If anybody has an idea to solve that I would be happy,