NEWS update for 3.13.3
Post-release version bump
Make file references in sgml files source-dir capable

The file references were written as relative paths, which doesn't
work when the build directory isn't the same as the source directory.
This is the case during 'make distcheck'.
data-test-utils.c: Make sure Camel's provider dir exists during tests

The 'make distcheck' fails due to nonexistence of the Camel's provider
directory when running certain tests. Creating it, even left empty,
fixes the tests failure and makes it pass properly.