Description:
------------
Document sni support in openssl.

Since 5.3.2.

New SSL context options :

- SNI_enabled : Set to FALSE to disable SNI support (enabled by default)
- SNI_server_name : If not set, the server name will be guessed from the stream URL (e.g. https://example.com/ will use example.com as hostname.), else the given name will be used.

SNI is to SSL/TLS what the Host header is to HTTP : it allows multiple
certificates on the same IP address. As for HTTP virtual hosts, this should be totaly transparent in most cases.

Context options allows more control, e.g. :
 
$context = stream_context_create(array(
  'ssl' => array('SNI_server_name' => 'foo.example.com'),
  'http' => array('header' => 'Host: foo.example.com'),
));
file_get_contents('https://127.0.0.1/', false, $context);

OpenSSL >= 0.9.8j supports SNI (by default since OpenSSL 0.9.8k).

New constant :

OPENSSL_TLSEXT_SERVER_NAME is defined if there is support for SNI.