Fix Google_IO_{Curl,Stream} setOptions

Fix Google_IO_{Curl,Stream} setOptions
- array_merge fores reindex on associative array, nuking the keys. + (union) operator for arrays specifically does the intended behavior of preserving the keys.

This took me for a bit of a loop -- I had upgraded our google-api-php-client lib and was getting an error with curl_setopt when calling `setOptions(array(CURLOPT_PROXY => '...'));`

Doing a var_dump() on $this->options revealed the keys had been turned into indexes by array_merge. I have verified everything works as desired when using the + (union) operator.

This blog post explains it well:
http://unix0.wordpress.com/2012/01/08/php-array_merge-vs-plus-union-operator/