cmdutil: replace unix pipe handshake with file lock
The pipe handshake cannot be implemented with Windows detached process, which
disables handle inheritance.
Fix 2/3 for issue421
#!/bin/sh
hg init a
cd a
mkdir a
echo a > a/b
hg ci -Am m
hg rm a
hg ci -m m a
mkdir a b
echo a > a/b
hg ci -Am m
hg rm a
cd b
# relative delete
hg ci -m m ../a