Merging from main trunk to release branch

I'm doing some testing and documentation in preparation for migrating
from CVS to Subversion.

I'm using svn, version 1.6.16 (r1073529) on Cygwin.

I'm having some difficulty with merging to release branches that I
haven't been able to find a solution for (other than continuing our old
CVS way of patching changes to active release branches).

The problem is this - there are inherently many changes between a
release branch and the main trunk (the older the release branch, the
more the number of changes). When we fix a bug and want to put the fix
in several releases, ONLY that change should be merged/patched.

So I made some changes in the trunk and committed them. I made some
changes that I expect to merge cleanly and some that I know will cause
conflicts due to differences between the code in the main trunk and
older release branches.

I then tried various different ways of merging just that change to a
release branch. I tried (all while in the top of the working copy of the
target branch):

          svn merge -c 9840 $SVNHVAURL/argus/trunk

          svn merge -r 9839:9840 $SVNHVAURL/argus/trunk

          svn merge $SVNHVAURL/argus/trunk_at_9839
$SVNHVAURL/argus/trunk_at_9840

and a bunch of other ways as well (including using the trunk's working
copy as the source).

In all the cases, the conflicts that showed up included all of the
differences between the trunk and the branch (including in sections of
the affected files that weren't anywhere near any of the test changes
and so therefore didn't need to be merged).

As a comparison I tried:

          svn diff -r 9839:9840 $SVNHVAURL/argus/trunk

That actually showed me just the changes that had been made. So the
question is how to get merge to apply just what svn diff shows and not
try to bring the release branch all the way up to the code that is in
the trunk? If I can't find a way to do that reliably, we'll be forced to
sticking with patch L

-- 
Steve Rothkin 
Honeywell, Inc. 
555 Pleasantville Road, North Bldg Suite 205 
Briarcliff Manor, NY 10510 
Office: 914-747-7198
Home: 914-762-4566
Cell:    914-420-3235