(See below for important information for anyone following my SVN repository)
I've decided to replace SLV2 with a new library (named "Lilv") instead of breaking the API which has been causing a lot of hassle, and would only cause more when it gets released and packaged. Among other things, this gives me the opportunity to rework the installation to support parallel installs of different major versions to prevent this kind of problem in the future. It also gives me a chance to improve the API and remove some cruft that has accumulated to avoid breaking the API (SLV2 has been around for many years now, and LV2 (and myself) have come a long way since then, it's a good time to do some laundry).
Anyone who has an SVN version of SLV2 installed, please uninstall it immediately and pretend it never existed. SLV2 0.6.6 is the last version of SLV2. The first Lilv release will be out shortly.