Fix PreferSsl

It'd be nice to have more robust testing for the SSL logic, but it seems
to be working.
Closes rust-postgres#15

Author: sfackler

lib.rs

@@ -406,8 +406,12 @@ fn initialize_stream(host: &str, port: Port, ssl: SslMode)
 
     let resp = socket.read_u8();
 
-    if resp == 'N' as u8 && ssl_required {
-        return Err(NoSslSupport);
+    if resp == 'N' as u8 {
+        if ssl_required {
+            return Err(NoSslSupport);
+        } else {
+            return Ok(Normal(socket));
+        }
     }
 
     match SslStream::try_new(ctx, socket) {

test.rs

@@ -25,6 +25,7 @@ use lib::{PostgresNoticeHandler,
           PostgresStatement,
           ResultDescription,
           RequireSsl,
+          PreferSsl,
           NoSsl};
 use lib::error::hack::{SyntaxError,
                        InvalidPassword,
@@ -571,13 +572,21 @@ fn test_cancel_query() {
 }
 
 #[test]
-fn test_ssl_conn() {
+fn test_require_ssl_conn() {
     let ctx = SslContext::new(Sslv3);
     let conn = PostgresConnection::connect("postgres://postgres@localhost",
                                            RequireSsl(&ctx));
     conn.update("SELECT 1::VARCHAR", []);
 }
 
+#[test]
+fn test_prefer_ssl_conn() {
+    let ctx = SslContext::new(Sslv3);
+    let conn = PostgresConnection::connect("postgres://postgres@localhost",
+                                           PreferSsl(&ctx));
+    conn.update("SELECT 1::VARCHAR", []);
+}
+
 #[test]
 fn test_plaintext_pass() {
     PostgresConnection::connect("postgres://pass_user:password@localhost/postgres", NoSsl);