ClosePipeStream failure ignored in pg_import_system_collations

Hackers,

I only see three invocations of ClosePipeStream in the sources.
In two of them, the return value is checked and an error is raised
if it failed. In the third, the error (if any) is squashed.

I don't know if a pipe stream over "locale -a" could ever fail to
close, but it seems sensible to log an error if it does.

Thoughts?

mark