Add NODE_DEBUG info to child_process

[remixz]

Fixes GH-720. Also adds the arguments passed to the Error object.

Example:

var spawn = require('child_process').spawn;
var path = require('path');

var child = spawn('fdjslkdf', ['--foo', 'bar'], {
  cwd: path.join(process.cwd(), './bat')
});

child.on('error', function (err) {
  throw err;
});

$ NODE_DEBUG=child_process ./iojs tmp.js
CHILD_PROCESS 72525: command: fdjslkdf
CHILD_PROCESS 72525: arguments: --foo,bar
CHILD_PROCESS 72525: options: {"cwd":"/Users/zach/Documents/github/remixz/io.js/bat"}
/Users/zach/Documents/github/remixz/io.js/tmp.js:9
  throw err;
        ^
Error: spawn fdjslkdf ENOENT
    at exports._errnoException (util.js:738:11)
    at Process.ChildProcess._handle.onexit (child_process.js:1029:32)
    at child_process.js:1120:20
    at process._tickCallback (node.js:337:11)
    at Function.Module.runMain (module.js:489:11)
    at startup (node.js:111:16)
    at node.js:799:3

[cjihrig]

Missing a semicolon

[remixz]

@cjihrig All done! Rebased into a967948.

[cjihrig]

Can you move the slice(1) from below to this line so that it's only called when an error occurs.

[cjihrig]

@trevnorris what do you think?

[trevnorris]

I'm cool with this. Except for the debug() call, it only affects error cases. And this isn't a hot code path anyways. LGTM.

@cjihrig want to clean up the commit and land it, or shall I?

[cjihrig]

I'll land it.

[cjihrig]

Thanks! Landed in 9a8f186. I tweaked the commit message and moved the debug('spawnSync' up a few lines to avoid printing the environment data too.

[rvagg]

@cjihrig @trevnorris should this have landed with a test too? It doesn't look trivial enough to me to not include a new test to help prevent regressions.

Reopening but please feel free to close if you have another perspective.

[trevnorris]

@rvagg The change isn't going to break existing functionality, but we could add a test to make sure the correct values are being attached to the error object.

[cjihrig]

I'll add the test for the error objects.

[cjihrig]

Test landed in d53b636