Add SSLv2 support behind a cfg flag

Many OpenSSL distributions have SSLv2 support compiled out, so it should
be opt-in.

ssl/ffi.rs

@@ -111,6 +111,8 @@ extern "C" {
 
     pub fn SSL_library_init() -> c_int;
 
+    #[cfg(sslv2)]
+    pub fn SSLv2_method() -> *SSL_METHOD;
     pub fn SSLv3_method() -> *SSL_METHOD;
     pub fn TLSv1_method() -> *SSL_METHOD;
     pub fn SSLv23_method() -> *SSL_METHOD;

ssl/mod.rs

@@ -38,15 +38,29 @@ fn init() {
 
 /// Determines the SSL method supported
 pub enum SslMethod {
+    #[cfg(sslv2)]
+    /// Only support the SSLv2 protocol
+    Sslv2,
     /// Only support the SSLv3 protocol
     Sslv3,
     /// Only support the TLSv1 protocol
     Tlsv1,
     /// Support the SSLv2, SSLv3 and TLSv1 protocols
-    Sslv23
+    Sslv23,
 }
 
 impl SslMethod {
+    #[cfg(sslv2)]
+    unsafe fn to_raw(&self) -> *ffi::SSL_METHOD {
+        match *self {
+            Sslv2 => ffi::SSLv2_method(),
+            Sslv3 => ffi::SSLv3_method(),
+            Tlsv1 => ffi::TLSv1_method(),
+            Sslv23 => ffi::SSLv23_method()
+        }
+    }
+
+    #[cfg(not(sslv2))]
     unsafe fn to_raw(&self) -> *ffi::SSL_METHOD {
         match *self {
             Sslv3 => ffi::SSLv3_method(),

ssl/tests.rs

@@ -1,3 +1,4 @@
+use std::from_str::FromStr;
 use std::io::Writer;
 use std::io::net::tcp::TcpStream;
 use std::str;