Enable reactphp/async to work on PHP 5.3.6; ensure errors in correct order

[matthew-andrews]

Enable the parallel function to work on PHP 5.3.6 (running the unit tests just emitted segfaults).

Also I noticed that the order of $errors would not necessarily match up with the order of parallel tasks so I fixed that too.

(I tried to use Travis to recreate the bug on 5.3.6, but it doesn't support that version 😕).

[matthew-andrews]

Hi @cboden, sorry to bother you but have you had a chance to look at this? It'd be great to switch back on to the main library. Many thanks!

[cboden]

I'll take a look after my product launch on Monday.

[igorw]

Error handling is pretty much broken anyway because parallel aborts on the first error. It is highly recommended you stop using react/async and instead use promises. It is much more solid, composable, usable, and has an actual strategy for dealing with errors.

[igorw]

If you make a separate PR with only the changes for PHP 5.3.6, then I will merge it. But both old versions of PHP and react/async itself will not be maintained much longer. Use promises instead!

[matthew-andrews]

Understood - will use promises.

Thanks!