Fixed example `Generating a formatted HTTP Request from a Request object`

Putting requests post data into requests content. `$request->toString()` returns now the expected output with post parameters.
Merge pull request #1017 in master
Merge pull request #1016 from websafe/fix/zend.http.request.rst

Fixed example `Generating a formatted HTTP Request from a Request object...
Merge branch 'hotfix/1016' into develop

Forward port #1016