Bug 6647: Add changes file

changes/bug6647

+  o Minor bugfixes:
+     - Prevent rounding error in path bias counts when scaling
+       them down, and use the correct scale factor default.
+       Bugfix against 0.2.3.17-beta.
+     - Demote some path bias related log messages down a level
+       and make others less scary sounding.
+       Bugfix against 0.2.3.17-beta.