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
echo % initialize remote repo with branches
hg init remote
cd remote
echo a > a
hg ci -Ama
hg branch br
hg ci -Amb
echo c > c
hg ci -Amc
hg log
cd ..
echo % try cloning -r branch
hg clone -rbr remote local1
hg -R local1 parents
echo % try cloning -rother clone#branch
hg clone -r0 remote#br local2
hg -R local2 parents
echo % try cloning -r1 clone#branch
hg clone -r1 remote#br local3
hg -R local3 parents