Support file stream

hallo I think I found a forgotten code area ;)

[near this line](https://github.com/zendframework/zf2/blob/master/library/Zend/Http/Client/Adapter/Curl.php#L278)

if we have a file resource, the CURL adapter try to get the file size from the header "content-lenght".

we have on the $headers var a array like this

```php
array(7) {
  ["Host"]=>
  string(14) "127.0.0.1:5984"
  ["Connection"]=>
  string(5) "close"
  ["Accept-Encoding"]=>
  string(13) "gzip, deflate"
  ["User-Agent"]=>
  string(16) "Zend\Http\Client"
  ["Content-Type"]=>
  string(16) "application/json"
  ["Content-Length"]=>
  string(2) "26"
  ["content-type"]=>
  string(16) "application/json"
}
```

but he try it detect form the value with preg_match()

```php
foreach ($headers AS $k => $header) {
    if (preg_match('/Content-Length:\s*(\d+)/i', $header, $m)) {
        if (is_resource($body)) {
            $this->config['curloptions'][CURLOPT_INFILESIZE] = (int) $m[1];
        }
    unset($headers[$k]);
    }
}
```

If the old code has a reason so correct me

best regards