change ctx.throw() to no longer .expose 5xx errors. Closes #197

lib/context.js

@@ -72,7 +72,7 @@ var proto = module.exports = {
 
     var err = msg instanceof Error ? msg : new Error(msg);
     err.status = status || 500;
-    err.expose = true;
+    err.expose = err.status < 500;
     throw err;
   },
 

test/context/throw.js

@@ -10,6 +10,7 @@ describe('ctx.throw(msg)', function(){
       ctx.throw('boom');
     } catch (err) {
       assert(500 == err.status);
+      assert(false === err.expose);
       done();
     }
   })