clone: save hardlink state of util.copyfiles()
When trying to do hardlink-cloning, the os_link() call of the
first file tried already fails on Windows, if the source is on a
UNC path.
This change avoids calling os_link() for the rest of files, leaving
us with a *single* failed os_link() call per clone operation, if the
source can't do hardlinks.
#!/bin/sh
hg init a
cd a
hg init b
echo x > b/x
echo '# should print nothing'
hg add b
hg st
echo '# should fail'
hg st b/x
hg add b/x
echo '# should fail'
hg add b b/x
hg st
echo '# should arguably print nothing'
hg st b
echo a > a
hg ci -Ama a
echo '# should fail'
hg mv a b
hg st