Manuall impl Show for SqlState

The derive'd impl generates an incredibly bad implementation.

cc rust-lang/rust#20856

src/error.rs

@@ -13,7 +13,7 @@ use types::Type;
 macro_rules! make_errors {
     ($($code:expr => $error:ident),+) => (
         /// SQLSTATE error codes
-        #[derive(PartialEq, Eq, Clone, Show)]
+        #[derive(PartialEq, Eq, Clone)]
         #[allow(missing_docs)]
         pub enum SqlState {
             $($error,)+
@@ -41,6 +41,16 @@ macro_rules! make_errors {
                 }
             }
         }
+
+        impl fmt::Show for SqlState {
+            fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+                let s = match *self {
+                    $(SqlState::$error => stringify!($error),)+
+                    SqlState::Unknown(ref s) => return write!(fmt, "Unknown({:?})", s),
+                };
+                fmt.write_str(s)
+            }
+        }
     )
 }