There are mailing lists that show every commit made to a FreeBSD branch. Have a look through the archives of:
http://lists.freebsd.org/pipermail/svn-src-stable-9/
http://lists.freebsd.org/pipermail/svn-src-head/
Alternatively, you can install subversion, checkout the source tree, then go through the svn commit logs to see all the changes between two dates.