[Doc-SIG] docstring grammar

[Mark Hammond]

> I more had in mind:
> 
> if sys.doc_building:
>   # Normally critical we do this.
>   dont_do_something_really_expensive()

Sheesh - I obviously meant:

if not sys.doc_building:
  do_something_really_expensive()

But Im sure you got my drift :-)

Mark.