Avoiding massive merges

[John Levon]

We have a Xen 3.0.4 tree, like this:

   | xen
   |
   |\ 3.0.4-branched
   | \
   |  \
   |   \_ 3.0.4 (our tree)
   |
   |
   |\ 3.1-branched
   | \
   |  \_ 3.1


Moving from the branched 3.0.4 to the branched 3.1 involves a ginormous
merge. Any suggestions for a strategy? I think I need an 'hgmerge' that
simply accepts the new version of the clashing files, or is there a
better way?

What do other people do in such circumstances?

thanks
john