Implemented popen(), pclose() functions.

[comm644]

Changes contain popen()/pclose() implementation. Please integrate it and add unit-tests. (code already working in our production build) New code added as hack without updating runtime.cmake , may be need fix it.

test/example:

<?php
error_reporting(E_ALL);

$handle = popen('/bin/ls', 'r');
echo "'$handle'; " . gettype($handle) . "\n";

while(($read = fread($handle, 512))) {
        echo "\nread: $read\n";
}
pclose($handle);