exclude A/a if B/a exists

[Daniel Becroft]

Hi,

Given the following folder structure:

/alpha
  foo.c
  bar.c
/beta
  foo.c
  A.txt

I am trying to construct a <fileset> definition to exclude any files in
/alpha if the same filename exists in /beta. That is, construct a <fileset>
that returns (from the above example):

/alpha/bar.c
/beta/foo.c
/beta/A.txt

At present, I'm creating a 'tmp-beta', and copying the contents of alpha,
then the contents of beta. However, with around 3500 files, this takes a
little time.

Can anyone suggest a cleaner method of creating this definition, or
achieving the same result?
---
Daniel Becroft