Comment 5 for bug 490212

Meld did not work as expected. Rather than working as INADA described for winmerge, you can pass a list of files to diff. So in order to handle both ways, I've come up with this sintax:

To launch so that process are launched simultaneously:
bzr diff --using "winmerge.exe &"

or to launch process with a list of all files:
bzr diff --using "meld [--diff @old_path @new_path]"
or
bzr diff --using "meld [--diff]"

WIP branch linked. Still need to do tests and documentation.