[m-rev.] for post-commit review: further improve parse_pragma.m

[Zoltan Somogyi]

On Thu, 16 Mar 2017 21:19:01 +1100 (AEDT), Julien Fischer <jfischer at opturion.com> wrote:
> >     Future proof some code against future changes that may make ContextPieces
> >     empty.
> 
> What future changes do you have in mind?

The addition of other calls to those functions.

There are several predicates in the compiler where some callers pass
nonempty context pieces, but other callers pass empty ones.
They were the reason why I added lower_case_if_not_first
to error_util.m in the first place.

Thanks for the review.

Zoltan.