RE: Allow escape in application_name

Dear Fujii-san,

> Attached is the patch that adds the regression test for
> postgres_fdw.application_name. Could you review this?
> 
> As Horiguchi-san suggested at [1], I split the test into two, and then tweaked them
> as follows.
> 
> 1. Set application_name option of a server option to 'fdw_%d%p'
> 2. Set postgres_fdw.application_name to 'fdw_%a%u%%'
> 
> 'fdw_%d%p' and 'fdw_%a%u%%' still may be larger than NAMEDATALEN
> depending on the regression test environment. To make the test stable even in
> that case, the patch uses substring() is truncate application_name string in the
> test query's condition to less than NAMEDATALEN.

I think it's good because we can care about max_identifier_length,
and both of setting methods are used.
Also it's smart using pg_terminate_backend().
(Actually I'm writing a test that separates test cases into five parts, but
your patch is better.)

I think the test failure should be noticed by me, but I missed, sorry.
Do you know how to apply my patch and test by buildfarm animals?

Best Regards,
Hayato Kuroda
FUJITSU LIMITED