This is from Ian – I am sure that it will make more sense when the time comes for me to use it :)
https://source.sakaiproject.org/svn/portal/branches/post-2-4
When you want to merge from trunk into a working copy of the branch. do…
to get the copy point do
svn log –stop-on-copy https://source.sakaiproject.org/svn/portal/branches/post-2-4
then merge will be
svn merge -rxxx:HEAD https://source.sakaiproject.org/svn/portal/trunk .
where xxx is the last copy point revision
into the working directory, followed by a commit.