proposal for a nice enhancement to "bzr diff --using <tool>"

[David Ingamells]

Presently bzr diff --using <meld|...> just prints the contents of new 
files and the old contents of removed files to the terminal and only 
uses the chosen (graphical) diff tool where there is an old AND a new 
file to compare. It is annoying to have to look both at the terminal and 
at the diff tool window (which pops up in front of the terminal) to 
review the changes. Further big files or lots of additions and removals 
can cause the scroll window of the terminal to overflow unless the bzr 
diff command is piped into "more" or "less".

It would be nicer IMHO if the removed and added files were also passed 
to the diff tool, but with an empty file to compare against as the first 
or second argument as appropriate.

Since my python and bzr internals knowledge is almost zero and 
absolutely zero respectively, I'll only be able to implement this myself 
(which I'm willing to do) if someone can point me at the right place in 
the code.