I think this is a general problem with rebase, not specific to 'merge --
rebase'.  It's annoying: if my current cset (first parent of working dir) is 
A and I run "hg merge B", then I get A=local and B=other.  But if I rebase A 
onto B, the relationship is backwards.  At the level of file merges, merging 
B with A should be the same as rebasing A onto B.