Fixed test-extdiff.
diff-like tools usually return 1 if differences are found.
Currently the extdiff returns 256, but that's a different topic
(consolidating return code handling in hg).
--- a/tests/test-extdiff
+++ b/tests/test-extdiff
@@ -23,4 +23,4 @@ hg ci -d '0 0' -mtest1
echo b >> a
hg ci -d '1 0' -mtest2
-hg falabala -r 0:1
+hg falabala -r 0:1 || echo "diff-like tools yield a non-zero exit code"
--- a/tests/test-extdiff.out
+++ b/tests/test-extdiff.out
@@ -29,3 +29,4 @@ options:
making snapshot of 1 files from rev e27a2475d60a
making snapshot of 1 files from rev 5e49ec8d3f05
diffing a.e27a2475d60a a.5e49ec8d3f05
+diff-like tools yield a non-zero exit code