Update to 4.0.0.

• Get rid of most of our patches: all the build fix patches are now unneeded, and the only ones we still have in files/ are there to either rename the xsd binary or install files into the right locations.

• Get rid of most bundled dependencies: use devel/build instead of the bundled copy, and libcutl via devel/libcutl. The only exception is libxsd-frontend, simply because its upstream is too horrible: it does not even contain a `make install' target.

• Expand the LICENSE part: the port is GPLv2-licensed, but also contains exceptions to allow its use with most free software licenses.

• Set CPPFLAGS, not CXXFLAGS, as the former's where we normally pass additional include paths.