Implement new array function array_column()

This pull request supersedes pull request #56. I have cleaned it up and have rebased branch PHP-5.3 onto my branch.

This pull request also includes new work as a result of feedback received on the original pull request and mailing list discussion.

References:

* https://wiki.php.net/rfc/array_column
* https://github.com/php/php-src/pull/56
* http://marc.info/?l=php-internals&m=134030710017255&w=2