Improving isolationtester's data output

I've been spending a lot of time looking at isolationtester results
over the past couple of days, and gotten really annoyed at how poorly
it formats query results. In particular, any column heading or value
that is 15 characters or longer is not separated from the next column,
rendering the output quite confusing.

Attached is a little hack that tries to improve that case while making
minimal changes to the output files otherwise.

There's still a good deal to be desired here: notably, the code still
does nothing to ensure vertical alignment of successive lines when
there are wide headings or values. But doing anything about that
would involve much-more-invasive changes of the output files.
If we wanted to buy into that, I'd think about discarding this
ad-hoc code altogether in favor of using one of libpq's fe-print.c
routines. But I'm not really sure that the small legibility gains
that would result are worth massive changes in the output files.

Thoughts?

regards, tom lane