Report from running bzr diff with difftools and tkdiff

[Stephen Ward]

I get the same error with bzr 0.12 using other diff tools, so it isn't 
specific to tkdiff.  So far, I haven't been able to reproduce this with any 
case that diffs against something in the current working tree, only with 
diffs between two old revisions.

Seems to be an interaction w/ lazy_import, in this case with mkdtemp from 
bzrlib.osutils.

I'll take a closer look at this later today.

-- Steve