HEAD revision with branches.

[Remi Gurski]

My local copy of file.c is checked out on my_branch (actually, the entire 
directory is on that branch), and has had several changes committed. There 
have also been changes committed to the mainline copy of file.c.

I want to see what the changes are between the tip of my_branch and the tip 
of mainline.
cvs diff -rHEAD file.c
doesn't work - it shows the diff between the local copy and the tip of 
my_branch. I guess that means HEAD is only the tip of the current branch?

How do I specify the "real" HEAD (i.e. the tip of the trunk?). Updating to 
the mainline copy of file.c and doing "cvs diff -rmy_branch" works, but can 
I do it the other way around (without adding a tag to the mainline just for 
a diff)?

(This is client 1.11 and pserver 1.11.2, if that matters).

Thanks,
- Remi