Workaround spawn bug in node v0.10.x

Workaround bugs in v0.10.x in which stdin was closed on EOF, and then future calls to spawn failed
because they were closing 0 due to a bug in libuv.  I submitted a PR to libuv, but they'd rather
workaround that bug in node, so the PR was rejected:

    https://github.com/joyent/libuv/pull/1162

We're working around the issue by opening a dummy fd=0