cxsc-2.5.4-bp156.3.6

- Drop unnecessary xz buildtime dependency

- Update to new upstream release 2.5.4
  * Linear system solver FastLss now accepts constant references
  * new function 'CompMat' for Ostrowski's comparison matrix
- Add cxsc-libversion.diff to set the right SO version

- Initial package (version 2.5.3) for build.opensuse.org