Update to 3.5.1.

Upstream changes are bugfixes:

  - Fix CMake configuration to allow build from released sources
    package (#753)
  - Fix memory leaks in single-sided buffers (#747), PlanarGraph and
    tests
  - Fix GeometryEditor to correctly update factory of empty geometries
    (#749)
  - Fix snapping of last segment of a closed linestring (#758)
  - Fix memory exhaustion case in isvalid (#757)
  - Fix Windows build with Visual Studio 2008 (#766)
  - Fix incorrect return from prepared multipoint intersects (#764)
  - Fix build against GCC 3.5.0+ (#784)

(gdt)