util.copyfiles: only switch to copy if hardlink raises IOError or OSError.
before this, interrupting clone would give "file a same as file b" error
because caught KeyboardInterrupt.
#!/bin/sh
hg init rep
cd rep
mkdir dir
touch foo dir/bar
hg -v addremove
hg -v commit -m "add 1" -d "1000000 0"
cd dir/
touch ../foo_2 bar_2
hg -v addremove
hg -v commit -m "add 2" -d "1000000 0"