[m-rev.] for post-commit review: fix a bug with require_switch_arms_detism

[Julien Fischer]

On Sun, 10 Apr 2016, Zoltan Somogyi wrote:

> For review by anyone.
>
> Zoltan.
>
> Fix a bug in handling require_switch_arms_detism.
> 
> compiler/cse_detection.m:
>     Don't pull unifications out of the arms of switches inside
>     require_switch_arms_detism scopes, since this can affect make
>     the scope ineffective, leading to error messages that should be
>     generated not being generated.
> 
> compiler/hlds_goal.m:
>     Fix some misleading variable names.
> 
> tests/invalid/require_switch_arms_detism.{m,err_exp}:
>     A regression test for the bug.
> 
> tests/invalid/Mmakefile:
>     Enable the new test.

That looks fine.

Julien.