Description:
------------
---
From manual page: http://www.php.net/oauth.fetch#refsect1-oauth.fetch-
description
---

this OAuth::fetch to option "array $http_headers"

Add value to existing header can not be
For example,
before

Authorization	OAuth 
oauth_consumer_key="vZtjt3BHU_Qu",oauth_signature_method="HMAC-
SHA1",oauth_nonce="10419861464f24f9a36b4e01.98191299",oauth_timestamp="132782326
7",oauth_version="1.0",oauth_token="MVySf_Nr_2WoTFkYMRvY_P72PdgOXn",oauth_signat
ure="bV%2F2VF4SF6dx0klduWfBf8GYptU%3D"

after

Authorization	OAuth realm="http://example.com", 
oauth_consumer_key="vZtjt3BHU_Qu",oauth_signature_method="HMAC-
SHA1",oauth_nonce="10419861464f24f9a36b4e01.98191299",oauth_timestamp="132782326
7",oauth_version="1.0",oauth_token="MVySf_Nr_2WoTFkYMRvY_P72PdgOXn",oauth_signat
ure="bV%2F2VF4SF6dx0klduWfBf8GYptU%3D"

If you want to change like that, do not change

$oauth->fetch($url, null, OAUTH_HTTP_METHOD_POST, 
array('Authorization'=>'realm'));