> That sounds reasonable.  So, can't we come up with a diff that does  
> both?  The base revision sounds like a completely necessary piece of  
> info.

I believe there is a bug report against Mercurial to include the base
revision even in git-style diffs, not sure what the status is. git itself
includes the base revision in its diffs; I believe that Mercurial didn't
dare to use the same syntax since the Mercurial hash wouldn't be a valid
git hash.