Your svn local copy should be replaced by a local fork of the git repository. Everything is explained on the Solarus github page, but to be short, use the following command to download the code (obviously, git needs to be installed):
git clone git://github.com/christopho/solarus.git
You now have a local fork of the repository, including the full history of commits. You may modify the code and even do your own local commits since git is a distributed versioning system. Then, if you want me to include your modifications into the official repository, you can make a request with git. Feel free to contribute!
Note: the SVN repository is still available but is now obsolete. New commits are only made on the Git repository. The SVN repository remains at revision 1443.