merge/patch from vendor repository

Hi all. Here's the situation, the vendor uses subversion, we use
subversion, unconnected repositories, we have read to thiers.

We have a vendor branch in ours, which has a certain revision of thier code
in it (an export from thier repository into
ours). We have modifications to that code in our trunk.

Now we want to bring in a new vendor drop, or specifically, we want to
apply to our trunk the changes from thier REV X to thier REV Y.

An svn diff won't do it, because the changes they have made over the last 6
months or so include binaries
(images) which wouldn't be included in a diff, and moving files (that we
want to keep history of so our changes don't get messy) etc.

Is there any way of doing this?

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James Sleeman