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
hg: config error at $HGRCPATH:1: 'invalid'
updating to branch default
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
[paths]
default = .../foo%bar
default = .../foo%bar
bundle.mainreporoot=.../foobar
paths.default=.../foo%bar
hg: config error at $HGRCPATH:2: ' x = y'
hg: config error at $HGRCPATH:1: cannot include /no-such-file (No such file or directory)