pipeline @param.output usage

This is a little strangeness. I'm not sure if this is anticipated behavior. If so, then it should be documented.

this works (passes the anticipated owi_obj):
```
@param.output(owi_obj=winds.OWI)
def output(self):
return self.execute()
```
This doesn't work (passes owi_obj as None):
```
@param.output(owi_obj=winds.OWI)
def owi_obj(self):
return self.execute()
```
And this doesn't work (passes owi_obj as None):
```
@param.output()
def owi_obj(self):
return self.execute()
```