Add a (q)uit option to the subr_blist test program.

[kib]

1. Please do not forget about the context for phab patches (-U99999999).
2. Please explain why this option is needed. For me it looks not too quiet, since the printf() at the beginning of the loop is still vocal.

[dougm]

If I use -U999999, I get one giant diff that I can't apply with 'patch' without collisions if anything changes. I thought -U15 was good enough, once.

Why is this needed? So that the test program isn't an infinite loop.

Why is this objectionable?

[kib]

In D20234#435979, @dougm wrote:

If I use -U999999, I get one giant diff that I can't apply with 'patch' without collisions if anything changes. I thought -U15 was good enough, once.

You only use that diff for upload to phab.

Why is this needed? So that the test program isn't an infinite loop.

Oh, I misread quit as quiet. Sorry.

Why is this objectionable?

It is in no way objectionable, I only try to understand your changes.