How do I remove a top-level directory from an SVN repository without losing history?

I have a SVN repository with the following layout:

trunk/somedir/a
             /b
             /[et cetera]

branches/branch1/somedir/a
                        /b
                        /[et cetera]

branches/branch2/somedir/a
                        /b
                        /c

where there are ~60 branches and about 17000 revisions in the whole repository. Unfortunately, local convention has been to keep svn:mergeinfo information on the somedir directories, rather than the root of the branch. This has created some diff开发者_StackOverflow社区iculties when trying to use parsing tools like Fisheye, and migration tools like git svn and the hg convertextension.

I can, of course, use svn move and reorder everything correctly - but I'd really like to do that over history, so that the conversion tools work more sanely. Do I have to write a custom tool for this, or is there a way to do this with svnadmin and svndumpfilter?

svn move is ok with history. But merges between branches will became difficult. (find why moves and renames are problematic in svn). I have similar problem and I wait until there was only trunk and reorganized repository structure in that moment. Merge-info (you can copy merge info from somedir to trunk. It is just svn properties.

I havent tried svnadmin tools, if You have succed with it let me now :)