tests/test-diffdir

util.copyfiles: don't try os_link() again if it failed before

If the os_link() call on the first file in the directory fails [1],
we switch mode to using shutil.copy() for all remaining files.

[1] happens for example on Windows for every file when cloning from a UNC
path without specifying --pull.

#!/bin/sh

hg init
touch a
hg add a
hg ci -m "a" -d "1000000 0"

echo 123 > b
hg add b
hg diff --nodates

hg diff --nodates -r tip

echo foo > a
hg diff --nodates

hg diff -r ""
hg diff -r tip -r ""

true