problem with extdiff extension

[James Walker]

The extdiff extension is not working for me lately, depending on which 
arguments I pass.  I'm using hg version 1.9.1 on Mac OS X 10.6.8.  My 
.hgrc enables extdiff and then configures it as follows:

[extdiff]
cmd.bbdiff=/usr/bin/bbdiff
opts.bbdiff=--wait --resume --reverse

Here bbdiff is a command that invokes the BBEdit text editor.

If I say

   hg bbdiff Source/StatusController.mm

then it works correctly.  If I say

   hg bbdiff -r 53 Source/StatusController.mm

then I get

   bbdiff: error: -36

where -36 is a Mac OS code that means I/O error.  And if I say

   hg bbdiff -r 53 -r 56 Source/StatusController.mm

then there is no response at all.

I suppose there could be a bug in bbdiff or BBEdit, which have been 
updated about as recently as Mercurial, but I'm not sure how bbdiff 
could tell the difference between these 3 cases.  In each case, it 
should just be receiving 2 files.

Any suggestions on how to proceed?