test-convert-darcs: skip if we can't find the elementtree module
This patch is a bit dirty to avoid having to repeat the dance required
to import elementtree.
% manifest of p2:
bar
foo
% manifest of p1:
foo
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
% this should not mention bar:
changeset: 3:ef2fc9b4a51b
tag: tip
parent: 2:ed1b79f46b9a
parent: 1:d394a8db219b
user: test
date: Thu Jan 01 00:00:00 1970 +0000
description:
merge
rev offset length base linkrev nodeid p1 p2
0 0 5 0 1 b004912a8510 000000000000 000000000000