uv-unix: fix build on systems that don't have pipe2()

Windows: correct comment in process.c

uv-unix: avoid exec-after-fork race in uv_spawn()

The race condition in a nutshell:

if ((pid = fork()) > 0) {
kill(pid, SIGTERM);
}
else if (pid == 0)

uv-unix: avoid exec-after-fork race in uv_spawn()

The race condition in a nutshell:

if ((pid = fork()) > 0) {
kill(pid, SIGTERM);
}
else if (pid == 0) {
execve("/bin/cat", argp, envp);
}

The parent sends a signal immediately after forking.
Since the child may not have called `execve()` yet,
there is no telling what process receives the signal,
our fork or /bin/cat.

To avoid ambiguity, we create a pipe with both ends
marked close-on-exec. Then, after the call to `fork()`,
the parent polls the read end until it sees POLLHUP.

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Support for unescaped arguments, suitable for use with cmd /c.

Robust argument escaping that hopefully matches Windows' algorithm for unescaping.

ev: fix infinite loop in ev_walk()

Windows: make process arguments buffer computation better

Windows: fix bug in process arguments buffer size computation

Windows: avoid errorneous freeing of pipe handle

unix: Remove flock code

solaris doesn't have flock

solaris fixes

Windows: report uv_spawn() failure asynchronously

windows: remove dependency on rpcrt4 and ole32 libs. fixes https://github.com/joyent/libuv/issues/118

fix spawn_and_kill test on windows

windows: fix for space in args

uv-unix: undo accidental revert of b700896 in 5ec2575

test: add platform-specific checks for kill-after-spawn test

test: make spawn_helper4 never return

Its whole raison d'être is to sleep until it's killed.

always use PATH from parent

unix: Add UV_READABLE, UV_WRITABLE flags; clean up uv_shutdown

test: exit with status code 1 in spawn_helper4

Fixes broken test spawn_and_kill.

test: move run-test spawn helpers to a separate function

windows: get values of path and pathext env variables when they're not supplied

uv-unix: unlock pipe after use, carry over lock file from uv_pipe_bind()

test: gets(3)? Just say no!

uv-unix: safely close pipe file descriptors