PathString argument exception that doesn't start with '/' should say so...

[HaoK]

                app.Map("always", map => { });

This currently gives you an extremely useless ArgumentException:

  System.ArgumentException :
  Parameter name: value
  Stack Trace:
       at Microsoft.AspNet.Http.PathString..ctor(String value)
       at Microsoft.AspNet.Http.PathString.op_Implicit(String s)

This should say PathStrings should start with '/' or something. I hit this when using Map

[Tratcher]

#251