Adapt to kdevplatform's PathFilter API changes
kdev-ruby compiles with this change (when combined with the build fixes in my previous two merge requests). All 5 tests that passed two months ago still pass. The duchain test fails in the same way as it did two months ago. Sorry, I haven't tested how this commit works, because I am not a Ruby developer and have zero experience with kdev-ruby.
See the commit message for details.